Understand HbS polymerization, sickling mechanisms, lab findings, and clinical crises for ASCP hematology MCQs.

ASCPprep.com | Hematology

Chapter 16 โ€” HEMOGLOBINOPATHIES (STRUCTURAL DEFECTS IN HEMOGLOBIN)

ASCP Board Exam ยท Lab-Focused Study Guide
Globin Genes & Hb Development ยท Mutations & Zygosity ยท Hb S (Sickle Cell Anemia & Trait) ยท Solubility Test ยท Alkaline & Acid Electrophoresis ยท HPLC ยท Hb C ยท Hb E ยท Hb O-Arab ยท Hb D & G ยท Hb SC & Other Compound Heterozygotes ยท Cis Mutations ยท Hb M ยท Unstable Hb ยท Altered Oโ‚‚ Affinity ยท Practice Questions

1 ยท Priority Table & Quick Foundation

Topic Priority Why It’s Tested
Hb S: ฮฒ6 Gluโ†’Val, polymerization, sickling mechanism HIGH Core mechanism (Rodak Q2)
Hb solubility (dithionite) test: principle, false positives and negatives HIGH Screening test pitfalls (Rodak Q10)
Alkaline vs acid (citrate agar) electrophoresis mobility HIGH Which Hbs comigrate and how to separate them (Rodak Q5, Q15)
Hb SS vs Hb AS vs Hb SC vs Hb S-ฮฒ-thal lab patterns (Table 27-2) HIGH % Hb values, morphology, severity (Rodak case study)
Sickle cell disease crises and complications (Box 27-3) HIGH VOC, aplastic (parvovirus), sequestration, megaloblastic, ACS (Rodak Q3, Q4, Q9)
Hb C: ฮฒ6 Gluโ†’Lys, hexagonal crystals, target cells HIGH Film identification (Rodak Q6)
Hb E: ฮฒ26 Gluโ†’Lys, microcytosis, Southeast Asia HIGH Microcytosis mimicking iron deficiency/thalassemia (Rodak Q13)
Punnett square inheritance; homozygous/disease vs heterozygous/trait HIGH Genetic counseling (Rodak Q8, Q11)
HPLC, capillary electrophoresis, IEF, neonatal screening MEDIUM Method strengths and comigration (Aโ‚‚/E)
Hb D, Hb G, Hb O-Arab, Hb C-Harlem, cis mutations (S-Antilles, S-Oman) MEDIUM Mobility traps; positive solubility with C-Harlem
Hb M (methemoglobinemia) and unstable Hb (Heinz bodies, isopropanol test) MEDIUM Brown blood; Heinz body anemia (Rodak Q7, Q16)
Hbs with increased/decreased Oโ‚‚ affinity (erythrocytosis vs cyanosis) MEDIUM Differential from polycythemia
Globin gene loci, Hb development, variant numbers (Table 27-1) LOW Background
๐ŸŽฏ KEY POINT โ€” Where to spend your time

Focus: the Hb S mutation and sickling triggers, solubility test pitfalls, which hemoglobins comigrate at alkaline pH (S/D/G; C/Aโ‚‚/E/O-Arab) and how acid pH separates them, % Hb patterns for SS, AS, SC, CC, EE and AE, SCD crises, Hb C crystals, SC crystals, and Punnett squares. Skim: global prevalence percentages, pulmonary hypertension statistics, biomarker lists, individual Hb M/unstable variant names beyond the classics (Kรถln, Zurich, Kansas).

Quick Foundation โ€” from zero

  • Hemoglobin = 4 globin chains (2 ฮฑ-like + 2 ฮฒ-like) each holding a heme. Adults: Hb A (ฮฑโ‚‚ฮฒโ‚‚) ~95%.
  • Hemoglobinopathy (structural, qualitative): normal amount of chain but the amino acid sequence is changed โ†’ altered structure/function. Thalassemia (quantitative): normal chain, reduced amount (next chapter).
  • Most variants are point mutations โ†’ one amino acid swapped. Whether it matters depends on the charge/size of the new amino acid, where it sits and how many genes are affected (zygosity).
  • Hb S: valine replaces glutamic acid at ฮฒ6 โ†’ deoxygenated Hb S molecules stick together into long polymers โ†’ the cell bends into a sickle.
  • Changing the charge changes electrophoretic mobility โ€” the basis of lab identification. Some different variants carry the same charge and run together, so a second method (acid pH, HPLC, solubility) is needed.
๐Ÿ’ก Analogy

Think of Hb molecules as marbles in a bag (the RBC). Normal marbles roll past each other. In Hb S, deoxygenation pops out a sticky tab (valine) that fits a slot on the next marble โ€” they snap together into long rods that stretch the bag into a crescent. Hb C marbles stack into short, thick bricks (crystals) that don’t bend the bag much. Electrophoresis is a race by charge: marbles with the same charge finish together even if they’re different colors โ€” so you rerun the race on a different track (acid pH).

๐Ÿฅ Why this matters clinically

Hemoglobinopathies are the most common genetic diseases (~7% of the world’s population; ~300,000 affected births per year). Newborn screening with prompt penicillin, vaccines and education sharply lowered childhood deaths from SCD. Misidentifying Hb D as Hb S (same alkaline position) or calling Hb E microcytosis ‘iron deficiency’ leads to wrong counseling and treatment.

Concept Plain-English Explanation
Hemoglobinopathy Structural (qualitative) Hb defect โ€” abnormal amino acid sequence
Thalassemia Quantitative defect โ€” reduced production of a normal globin chain
Homozygous / disease Both ฮฒ genes carry the same mutation (e.g., Hb SS)
Heterozygous / trait One mutated ฮฒ gene and one normal (e.g., Hb AS)
Compound heterozygote Two different mutations at the same locus (e.g., Hb SC, Hb S-ฮฒ-thal)
Double heterozygote Mutations at different loci (e.g., Hb SG โ€” ฮฒ and ฮฑ genes)
Cis mutation Two mutations on the same gene (e.g., Hb C-Harlem)
Comigration Different hemoglobins that run to the same spot on electrophoresis

2 ยท Core Content Tables

2.1 Globin Genes & Hemoglobin Development

Feature Details
ฮฑ-like genes ฮฑ and ฮถ on chromosome 16
ฮฒ-like genes ฮฒ, ฮณ, ฮด, ฮต on chromosome 11
Gene copies One copy per chromatid for each gene, except ฮฑ and ฮณ (two copies per chromatid โ†’ four per diploid cell). Genes: HBA1, HBA2 (ฮฑ), HBB (ฮฒ), HBG1, HBG2 (ฮณ), HBD (ฮด)
Embryonic (first 3 months) Gower-1 (ฮถโ‚‚ฮตโ‚‚) โ†’ Gower-2 (ฮฑโ‚‚ฮตโ‚‚) and Portland (ฮถโ‚‚ฮณโ‚‚)
Fetal ฮถ and ฮต stop โ†’ Hb F (ฮฑโ‚‚ฮณโ‚‚)
First 6 months after birth ฮณ gradually replaced by ฮฒ โ†’ Hb A (ฮฑโ‚‚ฮฒโ‚‚). BCL11A and KLF1 (zinc-finger repressors) silence ฮณ; their mutations raise Hb F
Around birth ฮด activated at low levels โ†’ Hb Aโ‚‚ (ฮฑโ‚‚ฮดโ‚‚)
Normal adult Hb A ~95% ยท Hb Aโ‚‚ <3.5% ยท Hb F <1โ€“2%

2.2 Types of Genetic Mutations (Table 27-1)

Feature Details
Scale >1000 structural variants; Table 27-1 lists 1181 (ฮฑ 435, ฮฒ 583, ฮด 66, ฮณ 97) plus 9 fusions
Point mutation Most common: one nucleotide replaced โ†’ one amino acid substitution; reading frame intact. 1109 of 1181. >35 variants have two point mutations in the same chain
Deletions / insertions Remove or add nucleotides. If not a multiple of 3 โ†’ frameshift โ†’ no chain (thalassemia). In hemoglobinopathies the frame usually stays intact โ†’ amino acids added/deleted (72 variants)
Chain extension Stop codon mutated โ†’ translation continues โ†’ longer chain; usually degraded (quantitative); if not โ†’ misfolding (qualitative)
Gene fusion Two genes break, swap and reanneal (e.g., ฮฒฮด and ฮดฮฒ fusion genes โ†’ hybrid chains; Hb Lepore = ฮดฮฒ fusion). 9 fusion chains known
Why ฮฒ variants matter more Two ฮฒ genes (vs four ฮฑ) and Hb A is ฮฑโ‚‚ฮฒโ‚‚ โ†’ one ฮฒ mutation affects more Hb. ฮณ and ฮด mutations matter little in adults

2.3 Pathophysiology & Classification

Feature Details
What determines impact Chemical nature (charge, size) of the substituted amino acid, its location in the chain, and zygosity
Homozygous ฮฒ variant Variant becomes the dominant Hb; no Hb A (e.g., Hb SS, Hb CC)
Heterozygous ฮฒ variant Expected 50/50 but variant usually present in lower amounts than Hb A (e.g., Hb AS, Hb AC)
Fishleder & Hoffman groups (1) Hemolytic anemia โ€” Hb S, unstable Hbs ยท (2) methemoglobinemia โ€” Hb M ยท (3) increased or decreased Oโ‚‚ affinity ยท (4) no clinical effect
Thalassemic phenotype Some structural variants reduce production too โ€” Hb Lepore, Hb E (ฮฒ-thal phenotype); Hb Constant Spring (ฮฑ-thal phenotype)

2.4 Nomenclature

Feature Details
Early Letters of the alphabet: Hb A, Hb F, Hb S, Hb Cโ€ฆ
Now Common name (usually place of discovery) + letter for mobility, e.g., Hb G-Philadelphia, Hb G-Copenhagen, Hb C-Harlem
Scientific Chain, position, helix and substitution: Hb S = ฮฒ6(A3) Gluโ†’Val โ€” glutamic acid replaced by valine at position 6 in the A helix of the ฮฒ chain

2.5 Clinically Important Hb Variants (Rodak Box 27-2 summary)

Group Examples
Sickle syndromes Sickle cell trait (AS); sickle cell disease: SS, SC, SD-Punjab (Los Angeles), SO-Arab, S-ฮฒ-thal, S-HPFH, SE
Unstable hemoglobins Congenital Heinz body anemia (>140 variants)
Abnormal Oโ‚‚ affinity High โ†’ familial erythrocytosis (>90 variants) ยท Low โ†’ familial cyanosis (Kansas, Beth Israel, Yoshizuka, Agenogi, Titusville, Providence)
M hemoglobins Familial cyanosis (9 variants: M-Boston, M-Iwate, Auckland, Chile, M-Saskatoon, M-Milwaukee-1, M-Milwaukee-2, F-M-Osaka, F-M-Fort Ripley)
Thalassemic phenotype ฮฒ: Hb Lepore, Hb E, Hb Indianapolisโ€ฆ ยท ฮฑ: chain termination mutants (Hb Constant Spring)

2.6 Hb S โ€” History, Inheritance & Prevalence

Feature Details
History Herrick 1910 (first report); Emmel 1917 (sickling in nonanemic people); Hahn & Gillespie 1927 (low Oโ‚‚ causes reversible sickling); Beet 1946 (fewer malaria parasites); Pauling 1949 (abnormal electrophoretic mobility โ€” first ‘molecular disease’)
Sickle cell diseases (SCD) Symptomatic sickling disorders: homozygous SS or compound heterozygotes (SC, S-ฮฒ-thalโ€ฆ). Most common: SS, SC, S-ฮฒ-thal
Inheritance ฮฒ-like variants: autosomal codominant, one gene from each parent. SS more severe than SC or S-ฮฒ-thal; AS generally asymptomatic
Highest frequency Sub-Saharan Africa: ~230,000 SS births/year (0.74% of live births). North America ~2600/yr; Europe ~1300/yr; India ~25,000/yr
Five main regions Sub-Saharan Africa, Arab-India, Americas, Eurasia, Southeast Asia. Nigeria, India and DR Congo โ‰ˆ 50% of SS and AS neonates
Other groups Middle East, India, Mediterranean, Caribbean, Central and South America

2.7 Hb S โ€” Etiology & Pathophysiology

Feature Details
Mutation ฮฑโ‚‚ฮฒโ‚‚^6Gluโ†’Val: nucleotide 17 thymine โ†’ adenine in codon 6 (GAG โ†’ GTG*)
Charge Glu (โˆ’1) โ†’ Val (0) = net change +1 โ†’ altered electrophoretic mobility
Polymer seed Oxygenated: no hydrophobic pocket โ†’ soluble. Deoxygenation creates a hydrophobic pocket at Phe85 and Leu88 of an adjacent molecule โ†’ valine binds โ†’ polymer: 4-molecule core + outer layer of 10 = 14-strand helical fiber
Sickling threshold Homozygotes: Oโ‚‚ saturation <85% ยท heterozygotes (trait): <40%
Vicious cycle Polymers โ†’ viscous blood โ†’ slow flow โ†’ more hypoxia, โ†“ pH, โ†‘ 2,3-BPG (โ†“ Oโ‚‚ affinity) โ†’ more sickling โ†’ occlusion of capillaries/arterioles โ†’ infarction
Reversible sickle cells Biconcave when oxygenated, sickle on deoxygenation; enter microvasculature โ†’ thought to cause vaso-occlusion
Irreversible sickle cells Fixed shape (elongated, pointed ends on film); removed by the spleen
Dehydration Psickle channel opens at pOโ‚‚ <50 mm Hg โ†’ Caยฒโบ influx โ†’ Gardos channel โ†’ Kโบ efflux (+ Clโป) โ†’ water loss โ†’ โ†‘ MCHC โ†’ more polymerization. Kโบ/Clโป cotransporter (activated by dehydration, low pH, Hb S/C) adds to it
Membrane phospholipids Flippases inhibited, scramblase activated โ†’ phosphatidylserine (PS) exposed (2.1% of SS cells vs 0.2% normal) โ†’ binds thrombospondin (adhesion), activates coagulation, โ†“ survival; PS hydrolyzed by sPLAโ‚‚ โ†’ lysophospholipids โ†’ vascular damage โ†’ acute chest syndrome

2.8 SCD โ€” Severity by Genotype & Onset

Feature Details
Severe (8 genotypes) SS, S-ฮฒโฐ-thal, severe S-ฮฒโบ-thal, SD-Punjab, SO-Arab, SC-Harlem, CS-Antilles, S-Quebec-CHORI
Moderate SC, moderate S-ฮฒโบ-thal, AS-Oman
Mild Mild S-ฮฒโบ-thal (silent), SE, SA-Jamaica Plain
Very mild S-HPFH, S with mild variants
Variability Mainly the intracellular Hb S : Hb F ratio, plus vessel tone and cellular activation; Indian patients milder
Onset Symptom-free until the second half of the first year โ€” protective Hb F; as ฮฒ (S) replaces ฮณ, hemolysis and splenomegaly appear

2.9 Clinical Features of SCD (Rodak Box 27-3)

Category Features
Vaso-occlusion โ€” triggers Acidosis, hypoxia, dehydration, infection, fever, extreme cold
Vaso-occlusion โ€” sites Bones (pain, hand-foot dactylitis, osteomyelitis) ยท lungs (pneumonia, acute chest syndrome) ยท liver (hepatomegaly, jaundice) ยท spleen (sequestration, autosplenectomy) ยท penis (priapism) ยท eyes (retinal hemorrhage) ยท CNS ยท urinary tract (renal papillary necrosis) ยท leg ulcers
Bacterial infections Sepsis, pneumonia, osteomyelitis
Hematologic Chronic hemolytic anemia ยท megaloblastic episodes ยท aplastic episodes
Cardiac Enlarged heart, murmurs
Other Stunted growth, high-risk pregnancy

2.10 SCD Crises & Complications

Feature Details
Vaso-occlusive crisis (VOC) Hallmark; most ER visits. Capillaries and postcapillary venules. Factors: polymerization, โ†“ deformability, sickleโ€“endothelial adhesion, endothelial, WBC and platelet activation, hemostatic activation, vascular tone. 0โ€“6 per year, 4โ€“5 days each
Hand-foot syndrome Children <3 years; painful swelling of hands and feet (dactylitis)
Splenic sequestration Sudden trapping of blood in the spleen โ†’ Hb often <6 g/dL; infants/young children with enlarged spleens; often with respiratory infection
Autosplenectomy Repeated splenic infarcts โ†’ loss of function โ†’ Howell-Jolly and Pappenheimer bodies; โ†‘ risk of encapsulated bacteria
Acute chest syndrome (ACS) Fever, chest pain, pulmonary infiltrates. Leading cause of death in adults; >10% die. sPLAโ‚‚ rises 24โ€“48 h before ACS
Pulmonary hypertension ~33% (10% severe); 40% mortality at 40 months. โ†“ nitric oxide (arginase from lysis degrades arginine; free Hb scavenges NO). Predictors: TRV >2.5 m/s*, NT-proBNP >160 ng/L. Treatment: bosentan
Bacterial infection S. aureus, S. pneumoniae, H. influenzae; most frequent cause of death especially in the first 3 years
Chronic hemolysis RBC survival 16โ€“20 days; โ†“ Hb, โ†‘ retics, jaundice, gallstones
Renal GFR >140 mL/min in 71%; microalbuminuria (>4.5 mg/mmol) โ†’ proteinuria โ†’ โ†‘ BUN/creatinine; ACE inhibitors
Megaloblastic episode Sudden arrest of erythropoiesis from folate depletion โ†’ prophylactic folic acid
Aplastic episode Most common life-threatening hematologic complication; usually parvovirus B19; Hct falls without reticulocyte response; recovery shows nRBCs and retics
Other Avascular necrosis of femoral/humeral head (~50% by age 35); leg ulcers (8โ€“10%); microstrokes (screen with transcranial Doppler); cardiomegaly

*Rodak cites ‘increased tricuspid regurgitation velocity (TRV)’; the 2.5 m/s cutoff is from general references.

2.11 Malaria & G6PD

Feature Details
Malaria Sickle gene frequency parallels P. falciparum; protects against cerebral malaria in young children. Parasites lower Oโ‚‚ in infected cells โ†’ sickling โ†’ trapped and phagocytized in spleen
G6PD deficiency Common in SCD; children with both had lower Hb, higher retics, 3ร— more acute anemia events, more transfusions. During aplastic crises the older (G6PD-deficient) cells dominate

2.12 SCD โ€” Laboratory Diagnosis

Feature Details
Anemia type Chronic hemolytic, normocytic, normochromic
Film Sickle cells (long curved cells, point at each end) and target cells (hallmark), nRBCs, a few spherocytes, basophilic stippling, Pappenheimer and Howell-Jolly bodies; marked poikilocytosis and anisocytosis
Retics / RDW Moderateโ€“marked polychromasia; retics 10โ€“25%; โ†‘ RDW. Aplastic crisis heralded by โ†“ retics
MCV Not as elevated as expected given the retic count
WBC / platelets Moderate leukocytosis (sometimes 40โ€“50 ร— 10โน/L) with neutrophilia and mild left shift; LAP not elevated in crisis alone (unlike infection); thrombocytosis usual
Marrow Erythroid hyperplasia
Other โ†‘ Immunoglobulins (esp. IgA); ferritin normal when young, โ†‘ later (hemochromatosis rare); โ†‘ indirect and total bilirubin
Hb pattern (SS) Hb A 0% ยท Hb S >80% ยท Hb F 1โ€“20% ยท Hb Aโ‚‚ 2โ€“5%. Hb F >20% modulates severity
S-ฮฒโฐ-thal vs SS Hb Aโ‚‚ quantitation โ€” โ†‘ in S-ฮฒโฐ-thal
Two-step diagnosis (1) Show insolubility of deoxy Hb S (solubility test) โ†’ (2) confirm by electrophoresis, HPLC or capillary electrophoresis; IEF, tandem MS or DNA for complex cases
Biomarkers WBC predicts events/mortality; CRP and sPLAโ‚‚ โ†‘ in VOC and ACS; IL-6, IL-10, VCAM-1, sPLAโ‚‚ most promising; annexin A5, MDA, ฮฑ-tocopherol

2.13 Hemoglobin Solubility Test

Feature Details
Principle Deoxygenated Hb S is insoluble โ†’ turbid solution
Reagents Buffered salt solution + reducing agent sodium hydrosulfite (dithionite) + detergent lysing agent saponin
Mechanism Saponin lyses RBC membranes โ†’ Hb released; dithionite converts Hb to the deoxygenated form*; deoxy Hb S polymerizes โ†’ turbid (lines behind the tube not visible); nonsickling Hbs โ†’ clear
False positive Hyperlipidemia, a few rare hemoglobinopathies, too much blood added
False negative Infants <6 months (high Hb F), low hematocrit
Other positive Hbs Hb C-Harlem (C-Georgetown), C-Ziguinchor, S-Memphis, S-Travis, S-Antilles, S-Providence, S-Oman, Alexander, Porte-Alegre โ€” all carry the ฮฒ6 Gluโ†’Val plus another substitution
Negative Hbs to remember Hb C, Hb E, Hb O-Arab, Hb D, Hb G (migrate with S but don’t sickle)
Older slide test 2% sodium metabisulfite under a sealed coverslip โ†’ sickle cells seen microscopically; slow, rarely used
Limitation Screening only โ€” does not distinguish AS from SS or SC

*Rodak’s text says dithionite ‘reduces the iron from the ferrous to the ferric oxidation state.’ That is chemically inconsistent (reduction goes ferric โ†’ ferrous); dithionite is a reducing agent that strips oxygen. For the exam, remember: dithionite deoxygenates Hb โ†’ Hb S becomes insoluble.

2.14 Hemoglobin Electrophoresis & Other Methods

Feature Details
Alkaline (pH 8.4โ€“8.6) Cellulose acetate (historical) or agarose. Hbs negatively charged โ†’ migrate to the anode (+). First step in confirmation
Alkaline order (origin โ†’ anode) Origin / carbonic anhydrase ยท Aโ‚‚ = C = E = O-Arab ยท S = D = G ยท F ยท A (fastest)
Acid (citrate agar pH 6.0โ€“6.2) Separates the alkaline comigrators: C separates from Aโ‚‚/E/O-Arab; S separates from D and G. Order in Rodak Fig. 27-7: C ยท S ยท origin ยท A (with D, G, E, O-Arab) ยท F
Hb O-Arab on acid Only Hb to move just slightly from the origin toward the cathode
HPLC Cation-exchange column; one injection; quantitates low levels of Aโ‚‚ and F โ†’ best for thalassemia; Aโ‚‚ and E comigrate; also used for Hb A1c; S appears in the ‘S window’
Capillary electrophoresis Charge-based in alkaline buffer; small volumes, better separation, automated (e.g., Capillarys โ€” 8 samples in parallel), โ‰ฅ3000 runs per capillary
Isoelectric focusing (IEF) Confirmatory; pH gradient โ€” Hb stops at its isoelectric point; resolves pI differences of 0.02; expensive, needs skilled staff
Neonatal screening Multisystem: adapted IEF, HPLC and reversed-phase HPLC; most common screen = HPLC confirmed by electrophoresis and genotyping
Reference methods Mass spectrometry, MALDI-TOF, IEF, DNA analysis
Most used (2009) Agarose electrophoresis; capillary and HPLC gaining

2.15 SCD โ€” Treatment

Feature Details
Supportive Hydration ยท prophylactic vitamins ยท avoid low-Oโ‚‚ settings (high altitude, unpressurized flights, strenuous exercise) ยท analgesia ยท aggressive antibiotics at first sign of infection
Penicillin prophylaxis Oral penicillin V 125 mg twice daily by 3 months to 3 years; 250 mg twice daily 3โ€“5 years
Vaccines Heptavalent conjugated pneumococcal at 2, 4, 6 months; 23-valent at 2 years + booster at 5 years; routine vaccines; annual influenza from 6 months
Pain NSAIDs/acetaminophen, nefopam for mild; morphine for acute VOC; meperidine or tramadol for chronic. Watch for opioid tolerance and central sensitization (reduce dose, switch to methadone/buprenorphine)
Hand-foot syndrome Fluids and analgesics
Transfusion Periodic (โ‰ฅ8/yr) to prevent stroke, priapism, PHT, leg ulcers etc. ยท blood exchange transfusion for severe VOC and ACS ยท before surgery: Hb S <50% or Hb 10 g/dL ยท pregnancy. Risks: reactions, infection, iron overload (most frequent)
Iron chelation Deferoxamine IV โ‰ฅ8 h/day for a week ยท deferasirox oral (FDA 2005)
Stem cell transplant HLA-identical related donor: 80โ€“90% event-free survival; cord blood ~90%; mainly children <17 with severe complications
Hydroxyurea (hydroxycarbamide) 25โ€“30 mg/kg daily; โ†‘ Hb F (doesn’t copolymerize with S). Hb F 12โ€“20% โ†’ little anemia; 5โ€“12% lessens hemolysis. Compliance: โ†‘ MCV; response: โ†“ LD. Predictors of response: high baseline Hb F, neutrophils, retics
Anti-dehydration Senicapoc (Gardos inhibitor), Mgยฒโบ (K-Cl cotransport) โ†’ โ†‘ Hb, โ†“ dense cells, no clear โ†“ VOC
Prognosis Life expectancy 14 years (1973) โ†’ ~50 years; Hb SC median 60 (men) and 68 (women)

2.16 Sickle Cell Trait (Hb AS)

Feature Details
Frequency ~8% of African Americans; also Central Americans, Asians, Mediterranean
Clinical Benign; normal life span. Severe hypoxia (unpressurized high-altitude flight, anesthesia, severe respiratory infection) โ†’ splenic infarcts, rare deaths
Only consistent abnormality Inability to concentrate urine (isosthenuria) โ€” reduced perfusion of the vasa recta; renal papillary necrosis with hematuria in some
Exercise Military recruits with trait: 21ร— greater risk of exercise-related death (46 documented cases)
Film Normal except a few target cells; normal WBCs and platelets
Labs Solubility positive; Hb S โ‰ค40% and Hb A โ‰ฅ60%; Aโ‚‚ normal or slightly โ†‘; F normal. S <40% lower with ฮฑ-thalassemia or iron/folate deficiency
Treatment None

2.17 Hemoglobin C

Feature Details
Discovery Next after Hb S; Hb CC described 1953 (Spaet & Ranney)
Prevalence 17โ€“28% in West Africa; 2โ€“3% of African Americans. Most common nonsickling variant in the U.S.; third most common worldwide
Mutation ฮฑโ‚‚ฮฒโ‚‚^6Gluโ†’Lys: lysine (+1) for glutamic acid (โˆ’1) = net +2
Pathophysiology Polymerizes under low Oโ‚‚ into short, thick crystals (not long polymers) โ†’ less RBC distortion, less sequestration and hemolysis; no vaso-occlusive crisis
Hb CC labs Mildโ€“moderate normocytic normochromic anemia (some microcytosis/hypochromia); marked target cells; slightโ€“moderate โ†‘ retics; nRBCs
Hb C crystals Hexagonal, dense, oblong with pyramid-shaped/pointed ends; inside RBCs or extracellular; seen on wet preps after washing and resuspending cells in sodium citrate
Hb % CC: no A, >90% C, F <7%, Aโ‚‚ ~2% ยท AC trait: ~60% A, ~30% C
Tests Solubility negative. Alkaline: C with Aโ‚‚, E, O-Arab; acid (citrate agar): separated
Treatment None specific; problems with infection or gallbladder disease from chronic hemolysis

2.18 Hemoglobin C-Harlem (C-Georgetown)

Feature Details
Mutation Two ฮฒ substitutions (cis): ฮฒ6 Gluโ†’Val (sickle) + ฮฒ73 Aspโ†’Asn (Korle Bu)
Name Migrates with Hb C at alkaline pH
Mobility Alkaline (cellulose acetate pH 8.4): C position ยท acid (citrate pH 6.2): S position
Solubility Positive
Clinical Heterozygotes asymptomatic; compound heterozygotes with Hb S (SC-Harlem) have crises like SS; homozygous outcome uncertain

2.19 Hemoglobin E

Feature Details
History / prevalence Described 1954; ~30% in Southeast Asia; increasing in the U.S. with immigration; rare in African Americans and whites
Mutation ฮฑโ‚‚ฮฒโ‚‚^26Gluโ†’Lys (+2); no polymerization
Thalassemic effect Codon 26 substitution creates a cryptic splice site โ†’ abnormal splicing โ†’ less functional ฮฒ^E mRNA โ†’ both qualitative and quantitative (ฮฒ-thal phenotype)
Malaria P. falciparum multiplies more slowly in EE cells โ€” possible protection (Thailand)
Hb EE Mild anemia, microcytes, target cells; shortened survival; no jaundice, hemolysis or splenomegaly. >90% Hb E, MCV 55โ€“65 fL, normal retics. Resembles thalassemia trait
Hb AE trait Asymptomatic; MCV ~65 fL, slight erythrocytosis, target cells, 30โ€“40% Hb E
Hb E-ฮฒ-thal Severe โ€” resembles ฮฒ-thalassemia major, needs transfusions
Differential Iron deficiency, ฮฒ-thal trait, Hb E-ฮฒ-thal
Tests Solubility negative. Alkaline: with C, O-Arab, Aโ‚‚. Acid: separated from C but comigrates with A and O-Arab. HPLC: E comigrates with Aโ‚‚
Treatment / counseling None; counsel like a mild ฮฒ-thal allele

2.20 Hemoglobin O-Arab

Feature Details
Mutation ฮฑโ‚‚ฮฒโ‚‚^121Gluโ†’Lys
Where Kenya, Israel, Egypt, Bulgaria; 0.4% of African Americans
Clinical Heterozygotes: no symptoms ยท homozygotes: mild hemolytic anemia, many target cells, solubility negative ยท with Hb S (SO-Arab): severe, like SS
Mobility Alkaline: with Aโ‚‚, C, E ยท acid: moves slightly toward the cathode โ€” separates from C
Treatment None usually needed

2.21 Hemoglobins D and G

Feature Details
Group โ‰ฅ16 ฮฒ-chain variants (Hb D) and 6 ฮฑ-chain variants (Hb G) that run with Hb S at alkaline pH (one less negative charge than A, like S)
Key point Do not sickle; solubility negative; separated from S on citrate agar pH 6.0. Suspect when a band in the S position has a negative solubility test
Hb D-Punjab = D-Los Angeles ฮฒ121 Gluโ†’Gln; ~3% of northwestern India; <2% of African Americans
Hb G-Philadelphia ฮฑ68 Asnโ†’Lys; most common G in African Americans (more frequent than D); also Ghana
Clinical Heterozygotes asymptomatic. Hb DD: mild hemolytic anemia, chronic nonprogressive splenomegaly; >95% D, normal Aโ‚‚ and F. Differentiate DD from D-ฮฒโฐ-thal by MCV, Aโ‚‚ and family studies

2.22 Compound Heterozygotes with Hb S & Cis Mutations

Genotype Key Features Lab Pattern
Hb SC Most common compound heterozygous syndrome; 25% in West Africa; ~1 in 833 U.S. births. Mild SCD; symptoms from teens; all VOC complications but less frequent; moderate splenomegaly; proliferative retinopathy more common; S. pneumoniae infections; morbidity after 30 Hb 11โ€“13 g/dL, retics 3โ€“5%; few sickle cells, target cells, SC crystals (blunt-ended, protrude from membrane; longer than C crystals, shorter/thicker than S polymers, often branched). Solubility +. ~45% S + ~45% C, F normal. Aโ‚‚ with C โ€” irrelevant except if C-ฮฒ-thal suspected
Hb S-ฮฒ-thal Most common sickle syndrome in Mediterranean people; second most common compound. S-ฮฒโฐ: like SS ยท S-ฮฒโบ: milder, like SC Hb S > Hb A (ฮฒโบ); โ†‘ Aโ‚‚ and F; microcytosis, hemolytic anemia, splenomegaly (vs trait: S < A)
Hb SD Compound heterozygote with D-Los Angeles (D-Punjab); mild to severe hemolysis, some severe VOC; treat like SCD ~45% S, 45% D; S and D comigrate at alkaline pH โ†’ acid pH needed. Film like milder SS
Hb SG-Philadelphia Double heterozygote (ฮฑ gene) โ†’ enough Hb A still made โ†’ asymptomatic ~45% S, 45% G; target cells; S and G comigrate alkaline
Hb S/O-Arab Severe chronic hemolysis with VOC; ฮฒ121 on the surface enhances S polymerization Mistaken for SC on alkaline (O-Arab runs with C); citrate agar separates
Hb S/D-Punjab Severe, like SCD Looks like SS at alkaline pH
Hb S-Korle Bu ฮฒ73 Aspโ†’Asn disrupts lateral contacts/hydrophobic pocket โ†’ inhibits polymerization โ†’ asymptomatic โ€”
Hb C-Harlem (cis) Sickle + Korle Bu mutations on the same gene; heterozygotes asymptomatic; SC-Harlem resembles SS Solubility +; alkaline C position; acid S position
Hb S-Antilles (cis) ฮฒ6 Gluโ†’Val + ฮฒ23 Valโ†’Ile โ†’ sickling even in heterozygotes Solubility +
Hb S-Oman (cis) ฮฒ6 Gluโ†’Val + ฮฒ121 Gluโ†’Lys โ†’ sickling in heterozygotes Solubility +

2.23 Common Clinically Significant Hemoglobinopathies (Rodak Table 27-2)

Disorder Structural Defect Solubility Hemoglobins Present RBC Morphology Treatment
Sickle cell anemia (SS) ฮฒ6 Gluโ†’Val Positive 0% A, >80% S, 1โ€“20% F, 2โ€“5% Aโ‚‚ Sickle cells, target cells, nRBCs, polychromasia, Howell-Jolly bodies, basophilic stippling Transfusions, antibiotics, analgesics, BMT, hydroxyurea
Hb C disease (CC) ฮฒ6 Gluโ†’Lys Negative 0% A, >90% C, <7% F, 2% Aโ‚‚ Hb C crystals, target cells, nRBCs, some microcytes Usually none; antibiotics
Hb SC-Harlem ฮฒ6 Gluโ†’Val + ฮฒ73 Aspโ†’Asn (same gene) + ฮฒ6 Gluโ†’Val Positive C-Harlem runs with C (alkaline), with S (acid) Target cells Similar to SS
Hb E disease (EE) ฮฒ26 Gluโ†’Lys Negative 0% A, 95% E, 2โ€“4% Aโ‚‚; with Aโ‚‚, C, O (alkaline) Target cells, microcytes Usually none
Hb O-Arab (homozygous) ฮฒ121 Gluโ†’Lys Negative 0% A, 95% O, 2โ€“4% Aโ‚‚; with Aโ‚‚, C, E (alkaline) Target cells Usually none
Hb D disease (DD) ฮฒ121 Gluโ†’Gln Negative 95% D, normal Aโ‚‚ and F; with S (alkaline) Target cells Usually none
Hb G disease ฮฑ68 Asnโ†’Lys Negative 95% G, normal Aโ‚‚ and F; with S (alkaline) Target cells Usually none
Hb SC ฮฒ6 Val + ฮฒ6 Lys Positive 45% S, 45% C, 2โ€“4% Aโ‚‚, 1% F Sickle cells, SC crystals, target cells Like SS, less intensive
Hb S-ฮฒ-thal ฮฒ6 Val + ฮฒโฐ or ฮฒโบ Positive S variable, some A in ฮฒโบ, โ†‘ Aโ‚‚ and F Sickle cells, target cells, microcytes Like SS; depends on Hb A
Hb SD ฮฒ6 Val + ฮฒ121 Gln Positive 45% S, 45% D, 2โ€“4% Aโ‚‚, 1% F; S and D comigrate Sickle cells, target cells Like SS, less intensive
Hb SG ฮฒ6 Val + ฮฑ68 Lys Positive 45% S, 45% G, 2โ€“4% Aโ‚‚, 1% F; S and G comigrate Target cells Usually none
Hb SO-Arab ฮฒ6 Val + ฮฒ121 Lys Positive 45% S, 45% O, 2โ€“4% Aโ‚‚, 1% F Sickle cells, target cells Like SS

2.24 Hemoglobin M (Methemoglobinemia)

Feature Details
Defect Mutations in ฮฑ, ฮฒ or ฮณ genes; most substitute tyrosine for the proximal (F8) or distal (E7) histidine โ†’ heme iron auto-oxidizes to ferric (Feยณโบ) โ†’ cannot carry Oโ‚‚ โ†’ cyanosis
Variants 7 ฮฑ/ฮฒ: ฮฑ โ€” M-Boston, M-Iwate, Auckland ยท ฮฒ โ€” Chile, M-Saskatoon, M-Milwaukee-1, M-Milwaukee-2 ยท ฮณ โ€” F-M-Osaka, F-M-Fort Ripley (symptoms disappear when A replaces F at 3โ€“6 months)
Inheritance Autosomal dominant; altered Oโ‚‚ affinity
Levels 30โ€“50% methemoglobin (normal <1%)
Clues Specimen looks brown; oxidant drugs (sulfonamides) can raise methemoglobin to life-threatening levels; Heinz bodies on wet preps
Diagnosis Spectral absorption of hemolysate (unique peaks per variant) or electrophoresis; first convert all Hb to methemoglobin with potassium cyanide; on cellulose acetate M runs slightly slower than A; use agar gel pH 7.1; confirm by HPLC or DNA
Treatment None; diagnose to avoid treating as cyanotic heart disease

2.25 Unstable Hemoglobin Variants

Feature Details
Nature >140 variants; most ฮฒ chain; ~25% cause hemolytic anemia; majority have โ†‘ Oโ‚‚ affinity
Names Formerly congenital nonspherocytic hemolytic anemia or congenital Heinz body anemia; now unstable hemoglobin disease
Inheritance Autosomal dominant; all patients heterozygous (homozygous incompatible with life)
Causes of instability (1) Charged for uncharged amino acid in the interior ยท (2) polar for nonpolar in the heme pocket ยท (3) substitution at ฮฑ-ฮฒ contact points ยท (4) proline in an ฮฑ helix ยท (5) deletion or elongation
Clinical Early childhood hemolytic anemia with jaundice and splenomegaly; fever or oxidant drugs worsen it. Hb precipitates as Heinz bodies โ†’ band 3 clustering, IgG binding, macrophage activation, splenic trapping
Examples Hb Kรถln (most prevalent), Hammersmith, Zurich (needs an oxidant for hemolysis), Gun Hill
Film Normal or slight hypochromia, prominent basophilic stippling
Labs Pre-splenectomy Hb 7โ€“12 g/dL, retics 4โ€“20%. After splenectomy: anemia corrected, reticulocytosis persists, Heinz bodies larger and more numerous. Dark urine (dipyrrole)
Heinz bodies Supravital stain; more with acetylphenylhydrazine incubation
Isopropanol test Isopropanol at 37 ยฐC weakens bonds: unstable Hb precipitates in 5 min, heavy flocculation by 20 min; normal Hb not until ~40 min
Heat test 50 ยฐC for 1 hour โ†’ flocculent precipitate with unstable Hb
Electrophoresis Many run in the normal AA pattern โ€” not detected. IEF, HPLC, DNA
Treatment Avoid sulfonamides and oxidants; splenectomy in severe cases; febrile illness can trigger hemolysis

2.26 Hemoglobins with Altered Oxygen Affinity

Feature Details
Background >150 variants; T (tense, deoxy) state = low Oโ‚‚ affinity, high 2,3-BPG affinity; R (relaxed, oxy) = high Oโ‚‚ affinity. Substitutions destabilizing T shift toward R โ†’ โ†‘ affinity
High affinity >90 variants; autosomal dominant; equal Hb A and variant (except with ฮฒ-thal: >85% variant). Hb doesn’t release Oโ‚‚ โ†’ tissue hypoxia โ†’ โ†‘ EPO โ†’ familial erythrocytosis; ruddy complexion, usually no symptoms; e.g., Hb Kempsey, Chesapeake
High affinity โ€” labs โ†‘ RBC, Hb, Hct; normal WBC, platelets and film; no hemolysis (unlike unstable Hbs). Electrophoresis may or may not show a band (citrate agar pH 6.0 helps); Oโ‚‚ affinity measurement (P50*) is definitive
High affinity โ€” management Normal life; no treatment; avoid misdiagnosis as polycythemia vera or secondary erythrocytosis
Low affinity Release Oโ‚‚ easily โ†’ normal to โ†“ Hb, slight anemia; cyanosis with normal arterial pOโ‚‚. Best known: Hb Kansas (ฮฒ102 Asnโ†’Thr). Detect by starch gel electrophoresis, HPLC or DNA

*P50 (the pOโ‚‚ at 50% saturation) is the standard affinity measure from general references; Rodak says ‘measurement of oxygen affinity’.

2.27 Global Burden

Feature Details
Scale ~7% of the world’s population; ~300,000 affected births per year
Trend As deaths from malnutrition and infection fall in developing countries, more affected patients survive and need care
Cyprus example Thalassemia prevalence rose after WWII; prenatal screening and counseling reduced affected births

3 ยท Visual Memory Hooks

๐Ÿง  Qualitative vs quantitative
โ€œHemoglobinopathy = wrong Hb; Thalassemia = too little Hbโ€.
๐Ÿง  Hb S vs Hb C
โ€œS = Six, Sticky Valine (V for Villain); C = Six, Lys (Crystal)โ€ โ€” both at ฮฒ6.
๐Ÿง  Hb E
โ€œE at 26 = East Asia, Extra small (microcytic)โ€.
๐Ÿง  Position 121
โ€œ121 club: D-Punjab (Gln), O-Arab (Lys), S-Oman (Lys)โ€.
๐Ÿง  Alkaline comigration
โ€œSDG runs together; CEOAโ‚‚ runs togetherโ€ (S/D/G and C/E/O-Arab/Aโ‚‚).
๐Ÿง  Alkaline order
โ€œA Fast Silly Catโ€ โ†’ from anode back: A, F, S, C.
๐Ÿง  Acid rescue
โ€œWhen in doubt, go Acidโ€ โ€” citrate agar separates S from D/G and C from E/O/Aโ‚‚.
๐Ÿง  Solubility test
โ€œDithionite Deoxygenates; S goes cloudyโ€ โ€” false + lipids/too much blood; false โˆ’ babies <6 mo, low Hct.
๐Ÿง  Sickling threshold
โ€œSS sickles at 85, AS at 40โ€ (% Oโ‚‚ saturation).
๐Ÿง  Dehydration channel
โ€œGardos Grabs Kโบ outโ€ โ†’ dehydrated dense cells.
๐Ÿง  SCD onset
โ€œFetal Hb is the Free pass for 6 monthsโ€.
๐Ÿง  SCD crises
โ€œVASAMโ€ โ€” Vaso-occlusive, Aplastic (parvovirus), Sequestration, Acute chest, Megaloblastic (folate).
๐Ÿง  Autosplenectomy
โ€œNo spleen โ†’ Howell-Jolly + Pneumococcusโ€.
๐Ÿง  Leading killers
โ€œKids die of Infection; Adults die of Acute chestโ€.
๐Ÿง  Hydroxyurea
โ€œHydroxyurea = Hb F Up, MCV Upโ€ (compliance marker).
๐Ÿง  Trait
โ€œTrait = 40/60 and can’t concentrate urineโ€.
๐Ÿง  Crystals
โ€œC = Hexagonal bar of gold; SC = blunt glove-finger crystalโ€.
๐Ÿง  C-Harlem
โ€œHarlem wears a C costume at alkaline, reveals S at acidโ€.
๐Ÿง  Hb D/G trap
โ€œS position + negative solubility = D or Gโ€.
๐Ÿง  SG
โ€œSG = So Goodโ€ โ€” ฮฑ-chain G leaves enough Hb A; asymptomatic.
๐Ÿง  Hb M
โ€œM = Methemoglobin, Mud-brown blood, Tyrosine replaces Hisโ€.
๐Ÿง  Unstable Hb
โ€œUnstable = Heinz, Isopropanol, Kรถlnโ€.
๐Ÿง  Oโ‚‚ affinity
โ€œHigh affinity = Hoards Oโ‚‚ โ†’ High Hct; Low affinity = Lets go โ†’ cyanosis (Kansas)โ€.

Pattern Triggers

If you seeโ€ฆ Thinkโ€ฆ Becauseโ€ฆ
Sickle cells + target cells, retics 10โ€“25%, Hb A 0%, S >80% Hb SS Homozygous ฮฒ6 Gluโ†’Val
Solubility +, S ~40%, A ~60%, normal film Sickle cell trait (AS) Heterozygous
S ~45%, C ~45%, blunt-ended crystals, target cells, Hb 11โ€“13 Hb SC (Rodak case study) Compound heterozygote
Sickle cells + microcytes, S > A, โ†‘ Aโ‚‚ Hb S-ฮฒโบ-thal Reduced ฮฒ^A production
Hexagonal crystals, many target cells, solubility โˆ’, C >90% Hb CC Lys crystals
Southeast Asian, MCV 60, target cells, normal ferritin, >90% band at Aโ‚‚/C position Hb EE ฮฒ26 cryptic splice โ†’ thal phenotype
Band in S position, solubility negative Hb D or Hb G Same charge, no sickling
Band in C position, solubility positive Hb C-Harlem Double substitution incl. ฮฒ6 Val
Alkaline ‘SC-like’ pattern, acid shows S + O Hb S/O-Arab O-Arab runs with C at alkaline pH
Brown blood, cyanosis from birth, normal heart, on sulfonamide Hb M Ferric heme iron
Hemolytic anemia, Heinz bodies, + isopropanol test, AD inheritance Unstable hemoglobin (e.g., Kรถln) Hb precipitates
High Hct, ruddy, normal WBC/platelets, family history High-Oโ‚‚-affinity Hb โ†‘ EPO from tissue hypoxia
Cyanosis with normal arterial pOโ‚‚ Low-Oโ‚‚-affinity Hb (Kansas) Releases Oโ‚‚ too easily
SCD child, Hb suddenly 4 g/dL, retics 0.5% Aplastic crisis (parvovirus B19) Erythropoiesis suppressed
SCD infant, Hb drop to 5, massive spleen Splenic sequestration crisis Blood trapped in spleen
SCD adult, fever, chest pain, new infiltrate Acute chest syndrome Leading adult cause of death
Solubility negative in a 3-month-old SS infant False negative (high Hb F) Too little Hb S

Commonly Confused Pairs

Feature A B
Hemoglobinopathy vs thalassemia Abnormal structure (qualitative) Reduced amount (quantitative)
Hb S vs Hb C ฮฒ6 Val, +1 charge, long polymers, sickles ฮฒ6 Lys, +2 charge, short crystals, no VOC
Hb SS vs Hb AS 0% A, >80% S, severe ~60% A, โ‰ค40% S, benign
Hb SS vs S-ฮฒโฐ-thal Normal-ish Aโ‚‚, normocytic โ†‘ Aโ‚‚, microcytic
Hb SC vs Hb S/O-Arab C separates on acid O-Arab separates on acid; more severe
Hb S vs Hb D/G Solubility +, sickles Solubility โˆ’, no sickling
Hb C crystal vs SC crystal Hexagonal, pointed ends, can be extracellular Blunt-ended, protruding, longer, branched
Hb E vs iron deficiency Normal ferritin, target cells, Hb E band โ†“ ferritin, pencil cells*
Compound vs double heterozygote Two mutations at same locus (SC) Different loci (SG: ฮฒ + ฮฑ)
Reversible vs irreversible sickle cells Change with Oโ‚‚; cause VOC Fixed; removed by spleen
Hb M vs unstable Hb Cyanosis, methemoglobin, brown blood Hemolysis, Heinz bodies
Unstable vs high-affinity Hb Hemolysis, abnormal morphology Erythrocytosis, normal morphology
HPLC vs electrophoresis Quantitates Aโ‚‚/F; E = Aโ‚‚ comigrate Charge separation; alkaline + acid

*Pencil cells in iron deficiency are from general references.

Timeline Table

Event Onset / Timing Key Point Best Exam Use
Embryonic Hbs First 3 months of gestation Gower-1 โ†’ Gower-2, Portland Hb development
Hb F โ†’ Hb A switch First 6 months after birth SCD symptoms start in 2nd half of year 1 Why infants are protected
Solubility false negative Infants <6 months High Hb F Screening pitfall
Penicillin prophylaxis By 3 months โ€“ 5 years 125 mg BID โ†’ 250 mg BID at 3โ€“5 yr Prevention
Pneumococcal vaccines 2, 4, 6 months; 2 yr; booster 5 yr Conjugate then 23-valent Prevention
Hand-foot syndrome <3 years Dactylitis Early presentation
Splenic sequestration Infants/young children Hb <6 g/dL Emergency
VOC episode 4โ€“5 days; 0โ€“6/year Most ER visits Clinical course
sPLAโ‚‚ rise 24โ€“48 h before ACS Predictor Biomarker
Avascular necrosis ~50% by age 35 Femoral/humeral head Complication
Hb F-M variants Resolve by 3โ€“6 months ฮณ-chain Hb M Hb M trap
Hb SC symptoms Teenage years Milder than SS Genotype comparison

4 ยท Diagnostic Flowcharts

Flowchart 1 โ€” Investigating a suspected sickle hemoglobinopathy

CBC + film (sickle cells? target cells? crystals?) โ†’ Hb solubility test
Solubility positive โ†’ Hb S (or rare sickling variant) present โ†’ quantitate by electrophoresis/HPLC
Alkaline electrophoresis / HPLC โ†’ Identify bands: A, S, C/E/O/Aโ‚‚ region, F
Ambiguous band โ†’ Citrate agar (acid pH) or IEF
Hb Aโ‚‚ / F quantitation, MCV, family study โ†’ Separate SS from S-ฮฒโฐ-thal; S-ฮฒโบ from AS
โš ๏ธ Common mistake: reporting ‘sickle cell disease’ from a positive solubility test โ€” it can’t tell AS from SS or SC.

Flowchart 2 โ€” Band in the S position on alkaline electrophoresis

Band at S โ†’ Solubility test
Solubility positive โ†’ Hb S โ†’ acid electrophoresis confirms S position
Solubility negative โ†’ Hb D or Hb G
Citrate agar pH 6.0 โ†’ D and G run with A, separated from S
Both S and D/G present โ†’ Hb SD (clinically significant) or Hb SG (asymptomatic)
โš ๏ธ Common mistake: calling Hb D trait ‘sickle trait’ because the band sits at S.

Flowchart 3 โ€” Band in the C position on alkaline electrophoresis

Band at C / Aโ‚‚ / E / O-Arab โ†’ Consider ethnicity, MCV, film, solubility
Solubility positive โ†’ Hb C-Harlem โ†’ acid: S position
Acid: C position โ†’ Hb C (hexagonal crystals, target cells)
Acid: with A, microcytosis, Southeast Asian โ†’ Hb E
Acid: slightly cathodal to origin โ†’ Hb O-Arab
Small amount (<3.5%) only โ†’ Hb Aโ‚‚ โ€” quantitate (โ†‘ in ฮฒ-thal trait)
โš ๏ธ Common mistake: assuming every band in the C position is Hb C โ€” E, O-Arab and Aโ‚‚ share it.

Flowchart 4 โ€” Acute event in a patient with SCD

Severe pain, normal retic response โ†’ Vaso-occlusive crisis โ†’ hydration, analgesia, Oโ‚‚; exchange transfusion if severe
Sudden โ†“ Hb + โ†“ retics โ†’ Aplastic crisis (parvovirus B19) โ†’ transfusion if severe
Sudden โ†“ Hb + โ†‘ retics + large spleen (child) โ†’ Splenic sequestration
Fever, chest pain, pulmonary infiltrate โ†’ Acute chest syndrome โ†’ exchange transfusion
โ†“ Hb + macrocytes/megaloblastic changes โ†’ Megaloblastic crisis โ†’ folic acid
Fever in a child โ†’ Presume bacterial sepsis (pneumococcus) โ†’ urgent antibiotics
โš ๏ธ Common mistake: missing an aplastic crisis because the patient is ‘always anemic’ โ€” the falling retic count is the clue.

Flowchart 5 โ€” Punnett square for two carriers

Parents AS ร— AS โ†’ Each passes A or S
Children โ†’ 25% AA ยท 50% AS ยท 25% SS
Parents SC ร— AS (Rodak case) โ†’ 25% AS ยท 25% SS ยท 25% AC ยท 25% SC
Parents AS ร— AA โ†’ 50% AA ยท 50% AS ยท 0% SS
Parents SS ร— AA โ†’ 100% AS
โš ๏ธ Common mistake: thinking a 25% risk means only one of four children will be affected โ€” each pregnancy carries the same risk.

Flowchart 6 โ€” Cyanosis, erythrocytosis or Heinz body hemolysis

Cyanosis + brown blood, low SpOโ‚‚ from birth, normal heart โ†’ Hb M โ†’ spectral absorption; KCN + agar gel pH 7.1
Cyanosis + normal arterial pOโ‚‚ โ†’ Low-affinity Hb (Hb Kansas)
Erythrocytosis, normal WBC/platelets, family history โ†’ High-affinity Hb โ†’ Oโ‚‚ affinity measurement
Hemolysis + Heinz bodies, AD inheritance โ†’ Unstable Hb โ†’ isopropanol test, heat test
Normal electrophoresis โ†’ Doesn’t exclude โ€” use IEF, HPLC, DNA
โš ๏ธ Common mistake: treating high-affinity Hb erythrocytosis as polycythemia vera.

5 ยท 25 High-Yield Facts

# Fact
1 Hemoglobinopathies are qualitative (structural) defects; thalassemias are quantitative defects.
2 ฮฑ and ฮถ genes are on chromosome 16; ฮฒ, ฮณ, ฮด and ฮต genes are on chromosome 11.
3 Normal adults have ~95% Hb A, <3.5% Hb Aโ‚‚ and <1โ€“2% Hb F.
4 Point mutation is the most common mutation type in hemoglobinopathies.
5 Hb S is ฮฑโ‚‚ฮฒโ‚‚ with valine replacing glutamic acid at ฮฒ6.
6 Deoxygenated Hb S polymerizes into long fibers that sickle the RBC.
7 Homozygous Hb S sickles below 85% Oโ‚‚ saturation; sickle trait below 40%.
8 SCD symptoms usually begin in the second half of the first year as Hb F falls.
9 Vaso-occlusive crisis is the hallmark of SCD; acute chest syndrome is the leading cause of adult death.
10 Aplastic crises in SCD are usually caused by parvovirus B19.
11 Megaloblastic episodes in SCD are prevented with prophylactic folic acid.
12 Autosplenectomy produces Howell-Jolly bodies and increases risk of encapsulated bacterial infection.
13 Hb SS shows 0% Hb A, >80% Hb S, 1โ€“20% Hb F and 2โ€“5% Hb Aโ‚‚.
14 The solubility test uses sodium dithionite and saponin; Hb S gives a turbid solution.
15 Solubility false negatives occur in infants under 6 months and with low hematocrit.
16 At alkaline pH, Hb S comigrates with D and G; Hb C comigrates with Aโ‚‚, E and O-Arab.
17 Citrate agar electrophoresis at acid pH separates Hb S from D/G and Hb C from E/O-Arab.
18 Sickle cell trait shows about 40% Hb S and 60% Hb A; inability to concentrate urine is the only consistent finding.
19 Hb C is ฮฒ6 Gluโ†’Lys and forms hexagonal crystals with many target cells.
20 Hb E is ฮฒ26 Gluโ†’Lys, common in Southeast Asia, and causes microcytosis (MCV 55โ€“65 fL in EE).
21 Hb SC is the most common compound heterozygous sickle syndrome, with ~45% S and ~45% C.
22 Hb C-Harlem has a positive solubility test and migrates with C at alkaline pH and with S at acid pH.
23 Hydroxyurea raises Hb F; increasing MCV indicates compliance.
24 Hb M variants cause methemoglobinemia and cyanosis with brown-colored blood.
25 Unstable hemoglobins form Heinz bodies and are detected by the isopropanol or heat stability test.
โญ EXAM TIP โ€” The single most testable pattern

Alkaline electrophoresis groups hemoglobins by charge: S = D = G and C = Aโ‚‚ = E = O-Arab. Resolve them with the solubility test (only S-containing Hbs such as S and C-Harlem are positive) and acid citrate agar. Then match % values: SS (0% A, >80% S), AS (~40% S, ~60% A), SC (~45/45), CC (>90% C), EE (>90% E, MCV 55โ€“65).

Quick Interpretation Table

Lab Finding Clinical Interpretation
18-year-old woman, Hb 10.9, retics 3.1%, 50.9% S + 49.1% C, target cells and SC crystals Hb SC disease (Rodak case study) โ€” confirm with solubility (+) and citrate agar
Alkaline: one band at C + small F; acid: two bands; solubility โˆ’; target cells; Indian child Hb CO-Arab (Rodak Q15)
S 38%, A 60%, Aโ‚‚ 3%, normal film Sickle cell trait
S 88%, F 8%, Aโ‚‚ 3%, A 0%, normocytic Hb SS
S 80%, Aโ‚‚ 6%, F 10%, A 0%, MCV 68 Hb S-ฮฒโฐ-thalassemia
Band at S, solubility negative, acid: runs with A Hb D or G trait
C 94%, F 3%, Aโ‚‚ 2%, hexagonal crystals Hb CC
Brown blood specimen, patient on sulfonamide, cyanosis Hb M (Rodak Q7)
Isopropanol: precipitate at 5 min, flocculation at 20 min Unstable hemoglobin

๐ŸŽด Flashcards โ€” Active Recall Practice

How it works: tap the card to flip it. Then mark it โœ“ Knew It or โœ— Review Again (buttons unlock after flipping). Use ๐Ÿ”€ Shuffle to randomize and ๐Ÿ Finish anytime โ€” your summary appears at the end, and you can drill only the cards you missed.

๐Ÿ“ Practice Quiz โ€” Test Your Knowledge

How it works: tap an answer for each case. You’ll get instant feedback with the full explanation and the examiner’s trap. Your final score appears once all 10 are answered.

๐Ÿชค Trap Questions โ€” Beat the Examiner

Harder on purpose. Each question targets a real misconception. After answering you’ll see the correct reasoning, the trap explained, why the examiner wrote it, and the wrong answer most students choose.

8 ยท Rapid Revision Sheet

๐Ÿ“– READ THIS 2 HOURS BEFORE YOUR EXAM

Genes & Development

  • ฮฑ, ฮถ on chr 16 ยท ฮฒ, ฮณ, ฮด, ฮต on chr 11
  • ฮฑ and ฮณ: 2 copies/chromatid
  • Gower-1 ฮถโ‚‚ฮตโ‚‚ ยท Gower-2 ฮฑโ‚‚ฮตโ‚‚ ยท Portland ฮถโ‚‚ฮณโ‚‚
  • F ฮฑโ‚‚ฮณโ‚‚ โ†’ A ฮฑโ‚‚ฮฒโ‚‚ by 6 months
  • Adult: A 95%, Aโ‚‚ <3.5%, F <1โ€“2%

Hb S Mechanism

  • ฮฒ6 Gluโ†’Val (+1 charge)
  • Deoxy โ†’ Phe85/Leu88 pocket โ†’ 14-strand polymer
  • SS sickles <85% sat ยท AS <40%
  • Psickle โ†’ Caยฒโบ โ†’ Gardos โ†’ Kโบ loss โ†’ dehydration
  • PS exposure โ†’ adhesion; sPLAโ‚‚ โ†’ ACS

SCD Clinical

  • Onset 2nd half of year 1 (Hb F)
  • VOC hallmark ยท hand-foot <3 yr
  • Sequestration Hb <6 ยท aplastic = parvovirus
  • Megaloblastic โ†’ folate ยท autosplenectomy โ†’ HJ bodies
  • ACS = adult killer ยท infection = child killer

SCD Lab

  • Normocytic normochromic ยท retics 10โ€“25%
  • Sickle + target cells, nRBC, HJ bodies
  • WBC โ†‘ (LAP normal) ยท platelets โ†‘
  • SS: A 0, S >80, F 1โ€“20, Aโ‚‚ 2โ€“5%
  • โ†‘ Aโ‚‚ โ†’ S-ฮฒโฐ-thal

Solubility & Electrophoresis

  • Dithionite + saponin โ†’ turbid = S
  • False +: lipids, too much blood ยท false โˆ’: <6 mo, low Hct
  • Alkaline: S=D=G ยท C=Aโ‚‚=E=O
  • Acid citrate agar separates them
  • HPLC quantitates Aโ‚‚/F; E=Aโ‚‚ comigrate

Treatment

  • Penicillin 125 mg BID (3 moโ€“3 yr) โ†’ 250 mg (3โ€“5 yr)
  • Pneumococcal 2, 4, 6 mo; 23-valent 2 & 5 yr
  • Exchange transfusion: severe VOC, ACS
  • Hydroxyurea 25โ€“30 mg/kg โ†’ โ†‘ F, โ†‘ MCV
  • HSCT 80โ€“90% ยท chelation for iron overload

Trait & Hb C

  • AS: 8% African Americans; ~40% S / 60% A
  • Isosthenuria ยท benign ยท 21ร— exercise death risk
  • Hb C: ฮฒ6 Lys (+2); 2โ€“3% African Americans
  • Hexagonal crystals, target cells, no VOC
  • CC >90% C ยท AC ~30% C

Hb E, O-Arab, D, G

  • E: ฮฒ26 Lys, SE Asia 30%, cryptic splice
  • EE: >90% E, MCV 55โ€“65 ยท AE: 30โ€“40% E
  • O-Arab: ฮฒ121 Lys; SO-Arab severe
  • D-Punjab: ฮฒ121 Gln ยท G-Phila: ฮฑ68 Lys
  • D/G: S position, solubility โˆ’

Compound & Cis

  • SC: 45/45, SC crystals, retinopathy, Hb 11โ€“13
  • S-ฮฒ-thal: microcytic, โ†‘ Aโ‚‚ and F
  • SD severe ยท SG asymptomatic
  • C-Harlem: C (alkaline) โ†’ S (acid), solubility +
  • S-Antilles, S-Oman sickle as heterozygotes

Hb M ยท Unstable ยท Affinity

  • Hb M: Tyr for His โ†’ Feยณโบ, brown blood, cyanosis
  • KCN + agar gel pH 7.1; spectral absorption
  • Unstable: AD, Heinz, Kรถln, isopropanol 5โ€“20 min
  • High affinity โ†’ erythrocytosis (Kempsey)
  • Low affinity โ†’ cyanosis (Kansas)

9 ยท Final Memory Map

  • ๐Ÿงฌ HEMOGLOBINOPATHIES
    • Foundations
      • Globin genes (chr 16, chr 11) ยท Hb development
      • Mutation types ยท zygosity ยท nomenclature
    • Hb S
      • ฮฒ6 Gluโ†’Val ยท polymerization ยท dehydration ยท PS exposure
      • SCD crises: VOC, aplastic, sequestration, ACS, megaloblastic
      • Lab: sickle/target cells, solubility, electrophoresis/HPLC
      • Treatment: penicillin, vaccines, transfusion, hydroxyurea, HSCT
      • Sickle trait: 40/60, isosthenuria
    • Other Common Variants
      • Hb C โ€” hexagonal crystals
      • Hb E โ€” microcytic, SE Asia
      • Hb O-Arab ยท Hb D ยท Hb G
    • Compound & Cis
      • SC ยท S-ฮฒ-thal ยท SD ยท SG ยท S/O-Arab ยท S-Korle Bu
      • C-Harlem ยท S-Antilles ยท S-Oman
    • Lab Methods
      • Solubility (dithionite) ยท alkaline vs acid electrophoresis
      • HPLC ยท capillary electrophoresis ยท IEF ยท DNA
    • Functional Variants
      • Hb M โ†’ methemoglobinemia
      • Unstable Hb โ†’ Heinz bodies
      • High/low Oโ‚‚ affinity โ†’ erythrocytosis/cyanosis



PreviousNext