Differentiate reactive from clonal thrombocytosis and identify clinical significance for ASCP hematology exam.

ASCPprep.com | Hematology & Hemostasis

Chapter 26 โ€” THROMBOCYTOPENIA AND THROMBOCYTOSIS

ASCP Board Exam ยท Lab-Focused Study Guide
Pseudothrombocytopenia ยท Decreased Production (Inherited, Neonatal, Acquired) ยท Immune Destruction: ITP, Drug-Induced, HIT, NAIT, Neonatal Autoimmune, PTP ยท Nonimmune: Pregnancy/HELLP, TTP & ADAMTS-13, HUS, DIC ยท Splenic Sequestration & Dilution ยท Reactive Thrombocytosis vs Essential Thrombocythemia ยท Practice Questions

1 ยท Priority Table & Quick Foundation

Topic Priority Why It’s Tested
Acute vs chronic ITP (Table 40-3) HIGH Classic age/antibody/treatment contrast (Rodak Q2, Q4)
HIT: PF4โ€“heparin IgG, timing, >30โ€“50% drop, thrombosis, lab tests (SRA gold standard, ELISA), treatment HIGH Case study; Rodak Q5
TTP: pentad, ADAMTS-13, ULVWF, normal PT/PTT vs DIC, plasma exchange HIGH Emergency recognition
HUS: children, Shiga toxin (E. coli O157:H7, Shigella), renal failure HIGH Rodak Q10
NAIT (HPA-1a) vs neonatal autoimmune thrombocytopenia (maternal ITP) HIGH Rodak Q3, Q9
Pseudothrombocytopenia (EDTA clumping, satellitism) HIGH First step in every low count
Inherited thrombocytopenias: May-Hegglin (MYH9, AD), WAS, TAR, Bernard-Soulier, CAMT MEDIUM Rodak Q1, Q8
Drug-induced mechanisms: drug-dependent (quinine), hapten (penicillin), autoantibody (gold) MEDIUM Rodak Q7
Reactive thrombocytosis vs essential thrombocythemia MEDIUM Platelet function and morphology differences
Posttransfusion purpura, pregnancy (gestational, HELLP) MEDIUM Specific clinical settings
Splenic sequestration, hypothermia, massive transfusion LOW Distribution/dilution
Kawasaki disease, exercise, rebound thrombocytosis LOW Occasional recall
๐ŸŽฏ KEY POINT โ€” Where to spend your time

Focus: the three mechanisms (production, destruction, distribution), acute vs chronic ITP, HIT timing and lab tests, TTP vs HUS vs DIC lab contrasts, NAIT vs neonatal autoimmune, reactive vs essential thrombocytosis. Skim: rare gene names in Table 40-1, incidence statistics, individual drug lists.

Quick Foundation โ€” from zero

  • Thrombocytopenia = platelet count below the reference interval (150โ€“450 ร— 10โน/L). It is the most common cause of clinically significant bleeding.
  • Low platelets cause small-vessel, mucocutaneous bleeding: petechiae, purpura, ecchymoses, nosebleeds, gum and GI bleeding.
  • There are only three reasons platelets fall: the marrow makes too few, the body destroys too many, or they are in the wrong place (spleen) or diluted.
  • Thrombocytosis = platelets above 450 ร— 10โน/L. Usually reactive (inflammation, iron deficiency, surgery, splenectomy); sometimes autonomous (myeloproliferative neoplasms, especially essential thrombocythemia).
  • The lab first rules out a false low count (clumps or satellitism in EDTA) by looking at the blood film.
๐Ÿ’ก Analogy

Platelets are fish in a lake. The count falls if the hatchery (marrow) stops producing, if predators (antibodies, clots, damaged vessels) eat them, or if they crowd into a side pond (enlarged spleen) or the lake is flooded with water (massive transfusion). A fake count happens when fish swim in schools that the counter reads as one big fish (EDTA clumping). Too many fish can mean a healthy lake after a storm (reactive) or a broken hatchery that won’t stop (essential thrombocythemia).

๐Ÿฅ Why this matters clinically

Some thrombocytopenias bleed (ITP, drug-induced), but others clot (HIT, TTP) โ€” giving platelets or continuing heparin in the wrong one can kill. TTP was >80% fatal before plasma exchange; now ~80% survive with early treatment. A falling count in a heparinized patient โ€” even inside the reference range โ€” may be HIT (the Rodak case).

Concept Plain-English Explanation
Pseudothrombocytopenia Falsely low count from EDTA-induced clumping or platelet satellitism around neutrophils
Petechiae / purpura / ecchymoses ~1 mm dots / ~3 mm spots / โ‰ฅ1 cm bruises
ITP Immune thrombocytopenia โ€” autoantibodies shorten platelet survival
HIT IgG against heparinโ€“PF4 complexes activates platelets โ†’ thrombocytopenia with thrombosis
NAIT Maternal alloantibody against a paternal platelet antigen (HPA-1a) on fetal platelets
TTP ULVWF multimers not cleaved (ADAMTS-13 deficiency) โ†’ plateletโ€“VWF microthrombi
HUS Shiga toxin damages renal endothelium โ†’ MAHA, renal failure, thrombocytopenia
Reactive thrombocytosis Temporary high count from an underlying condition; normal function
Essential thrombocythemia Clonal MPN with persistent, autonomous platelet production

2 ยท Core Content Tables

2.1 Thrombocytopenia โ€” Definitions & Bleeding Risk

Feature Details
Reference interval 150โ€“450 ร— 10โน/L (150,000โ€“450,000/ยตL)
Clinically important <100,000/ยตL โ€” most common cause of significant bleeding
Bleeding risk Rare above 50,000/ยตL; high risk (spontaneous, intracranial) below 10,000/ยตL
Skin lesions Petechiae ~1 mm ยท purpura ~3 mm ยท ecchymoses โ‰ฅ1 cm
First step Exclude pseudothrombocytopenia: EDTA platelet clumping or satellitism (platelets rosetting around neutrophils) โ€” check the film; recollect (e.g., citrate*)
Classification (Box 40-1) Decreased production ยท increased destruction (immune or nonimmune) ยท abnormal distribution or dilution

*Citrate recollection is standard lab practice; confirm wording against your full chapter.

2.2 Inherited Thrombocytopenias (Rodak Table 40-1 โ€” high-yield subset)

Disorder Gene / Inheritance Platelet Size Key Features
Wiskott-Aldrich syndrome / X-linked thrombocytopenia WAS ยท X-linked Small WAS: eczema and immunodeficiency*; XLT milder
MYH9-related: May-Hegglin, Sebastian, Fechtner, Epstein MYH9 ยท autosomal dominant Giant Dรถhle-like bodies in neutrophils; ยฑ deafness, cataracts, nephritis
Bernard-Soulier syndrome GP1BA, GP1BB, GP9 Giant GP Ib/IX/V missing (qualitative defect โ€” Ch. 27)
TAR (thrombocytopenia with absent radii) RBM8A (1q21.1) ยท autosomal recessive Normal Absent radii (forearm bone hypoplasia); leukemoid reactions ~90%; platelets 10โ€“30,000 in infancy; improves after 1st year
CAMT (congenital amegakaryocytic) MPL (TPO receptor) ยท AR Normal Platelets <20,000; evolves to marrow aplasia; cured by HSCT
Paris-Trousseau / Jacobsen 11q23 deletion Giant Giant ฮฑ-granules
GATA1-related X-linked Large ยฑ dyserythropoiesis
FPD/AML RUNX1 ยท AD Normal Predisposition to AML
Gray platelet syndrome NBEAL2 Large Gray, agranular platelets (ฮฑ-granule deficiency*)
Others ANKRD26 (~10%), ITGA2B/ITGB3, TUBB1, CYCS, FLNA, HOXA11 (CTRUS), ABCG5/8 (sitosterolemia) Varies Rare
Fanconi anemia Autosomal recessive* Normal Marrow failure; pancytopenia

*Starred features are general knowledge, not stated in the uploaded pages.

2.3 Neonatal & Acquired Production Defects

Feature Details
Neonatal thrombocytopenia <150,000/ยตL in 1โ€“5% of births; 75% present within 72 h
Most neonatal cases Placental insufficiency; immune (allo/auto) 15โ€“20% of consumptive cases; DIC 10โ€“15%
Congenital infections TORCH โ€” especially CMV; toxoplasmosis, rubella, HIV
Maternal drugs Chlorothiazide, tolbutamide
Drug hypoplasia Chemotherapy (IL-11/TPO used to treat), zidovudine, anagrelide, alcohol, interferon, estrogens, chloramphenicol
Ineffective thrombopoiesis Megaloblastic anemia (Bโ‚โ‚‚/folate) โ€” megakaryocytes present but platelets not released normally
Viral Live measles vaccine, CMV, VZV, rubella, EBV
Marrow replacement Leukemia, lymphoma, metastatic tumor, fibrosis

2.4 Acute vs Chronic ITP (Rodak Table 40-3)

Feature Acute ITP Chronic ITP
Age Children 2โ€“6 years Adults 20โ€“50
Sex Equal Female 2โ€“3:1
Onset 1โ€“3 weeks after viral infection Insidious
Platelet count <20,000/ยตL 30,000โ€“80,000/ยตL
Duration 2โ€“6 weeks Months to years
Spontaneous remission ~90% Uncommon
Season Winter/spring None
Antibody Probably immune complexes/viral Autoantibodies to GP IIb/IIIa or Ib/IX (50โ€“60%)
Treatment Usually none; IVIG if severe Prednisone; IVIG/anti-D; rituximab; splenectomy
Steroid response 70% 30%
Splenectomy โ€” 90% if <45 years; 40% if >45

2.5 ITP โ€” Key Details

Feature Details
Name “Idiopathic” โ†’ immune thrombocytopenia
Acute 4/100,000 children; 10โ€“15% become chronic (>6 months); 3โ€“4% severe; ICH mortality 1โ€“2%
Chronic 3.2โ€“6.6/100,000; spleen is main site of removal
Film Fewer but larger platelets (โ†‘ MPV) โ€” young, hyperfunctional
Marrow Megakaryocytic hyperplasia (NOT hypoplasia)
Therapy threshold Treat if <30,000/ยตL or bleeding
Prednisone 70โ€“90% respond, ~50% long term
Splenectomy 88% improve, 66% complete; vaccinate โ‰ฅ2 weeks before
Others IVIG, anti-D (Rh+ patients), rituximab, azathioprine

2.6 Drug-Induced Immune Thrombocytopenia

Mechanism Example Drugs Key Points
Drug-dependent antibody Quinine, quinidine, sulfa Fab binds GP Ib/IX/V or IIb/IIIa only when drug present; 1โ€“2 weeks after exposure; often <10,000/ยตL; “innocent bystander” immune complex theory abandoned
Antiplatelet agents Abciximab, tirofiban, eptifibatide Within hours โ€” naturally occurring antibodies
Hapten Penicillin and derivatives Small drug + carrier (plasma or platelet membrane protein) โ†’ complete antigen; may be <10,000 or even <1000/ยตL; hemorrhagic bullae in mouth
Drug-induced autoantibody Gold, procainamide, levodopa Antibody binds platelet GP with no drug needed; gold may persist months
Immune complex (HIT) Heparin IgG to heparinโ€“PF4; Fc activates platelet FcฮณIIa โ†’ thrombosis
Nonimmune direct Ristocetin, hematin, protamine, bleomycin Ristocetin โ†’ VWFโ€“GP Ib agglutination in vivo

Treatment: identify and stop the drug; IVIG; platelets only for life-threatening bleeding. Drugโ€“antibody dissociation may take 1โ€“2 weeks.

2.7 Heparin-Induced Thrombocytopenia

Feature Details
Incidence 1โ€“5% of patients on UFH
Type I (nonimmune) Rapid, mild (rarely <100,000/ยตL), transient; resolves even if heparin continues
Type II (immune) IgG to heparinโ€“PF4 neoepitope; Fc binds FcฮณIIa โ†’ activation โ†’ arterial/venous thrombosis
Timing Rodak Ch40: 7โ€“14 days after first exposure; 1โ€“3 days if prior exposure (Ch39 said 5โ€“10)
Count Typically not <40,000/ยตL; a >30% fall from baseline signals HIT even within reference range
Thrombosis 10โ€“30% โ€” gangrene, amputation, death
Heparin resistance Needing more heparin (PF4, ฮฒ-TG neutralize it) โ€” often precedes HIT
LMWH Less likely to cause HIT but cross-reacts โ€” not a substitute
Fondaparinux Does not bind PF4 โ€” off-label second-line option
Treatment Stop heparin AND substitute: DTIs argatroban, bivalirudin
Monitoring Daily platelet counts on UFH

2.8 HIT Laboratory Tests (Rodak Table 40-4)

Test Principle Performance
ELISA / immunoassays (PF4โ€“heparin) PF4โ€“heparin coated wells + patient serum โ†’ enzyme-labeled anti-human Ig โ†’ color โ†‘ Sensitivity, โ†“ specificity (detects nonpathogenic Ab); IgG-specific kits better; screen with 4Ts
Platelet aggregation (HIPA) Patient serum + normal donor PRP + heparin; monitor 20 min Specificity ~100%, sensitivity ~50%; donors aspirin-free 10โ€“14 days, same ABO
Serotonin release assay (SRA) Donor platelets loaded with radiolabeled serotonin + patient serum; release at therapeutic heparin, none at supratherapeutic Gold standard; radioactive; few labs
Platelet count >30% decrease from baseline Earliest clue

2.9 Alloimmune & Maternal Antibody Disorders

Feature NAIT Neonatal Autoimmune Posttransfusion Purpura
Antibody Maternal alloantibody vs paternal antigen on fetal platelets Maternal autoantibody (ITP, SLE) crosses placenta Recipient alloantibody
Antigen HPA-1a (80%), HPA-5b (10โ€“15%); HPA-3a (Bak) in Asians; HPA-4 Mother’s own platelet antigens HPA-1a (>90%)
Mother’s count Normal Low (ITP) โ€”
First pregnancy Yes โ€” ~50% of first-born affected (like HDFN) โ€” Multiparous middle-aged women
Severity Platelets <30,000; ICH or death ~25%, half in utero Only ~10% of infants affected; ICH โ‰ค1% Severe; ~1 week after transfusion; mortality ~10% untreated
Treatment Antigen-negative (maternal, washed) platelets ยฑ IVIG; weekly maternal IVIG in utero; C-section Usually none; IVIG/platelets/steroids if bleeding; C-section NOT recommended IVIG (2-day course)

2.10 Pregnancy-Associated Thrombocytopenia

Feature Details
Gestational (incidental) Most common; ~5% of pregnancies; 100โ€“150,000/ยตL (98% >70,000); no bleeding risk; normal weeks after delivery; recurs
Hypertensive disorders ~20% of pregnancy thrombocytopenia; preeclampsia ~5% of pregnancies after ~20 weeks
Preeclampsia Hypertension + proteinuria; thrombocytopenia in 15โ€“20%; 40โ€“50% of those progress to eclampsia (seizures)
HELLP Hemolysis, Elevated Liver enzymes, Low Platelets; 4โ€“12% of severe preeclampsia; low-grade DIC (โ†‘ D-dimer)
Treatment Deliver the infant; magnesium sulfate for seizures
Other causes ITP, HIV, SLE, APS, TTP (10โ€“25% of women with TTP present in pregnancy/postpartum), HUS
HDFN Moderate thrombocytopenia from RBC breakdown products โ€” antigen not on platelets

2.11 TTP vs HUS vs DIC

Feature TTP HUS DIC
Patients Women 30โ€“40 (F:M 2:1) Children 6 moโ€“4 yr (adult form exists) Any, with trigger
Cause ADAMTS-13 deficiency (autoantibody; congenital in chronic relapsing) โ†’ ULVWF Shiga toxin: EHEC O157:H7, Shigella dysenteriae (~90%) Sepsis, obstetric, trauma, cancer
Thrombi Platelets + VWF (little fibrin) Renal glomerular Platelets + fibrin
Platelets Severe โ†“ Mildโ€“moderate โ†“ โ†“
Schistocytes Marked (+ microspherocytes, keratocytes, NRBCs) Present, usually less ~50%
Kidney Dysfunction in >half, no anuria Renal failure, dialysis Variable
Neurologic Yes Absent Variable
PT/PTT/fibrinogen/D-dimer Normal Normal Abnormal (โ†‘ PT/PTT, โ†“ fibrinogen, โ†‘โ†‘ D-dimer)
Treatment Plasma exchange (FFP or cryo-poor plasma) + steroids; avoid platelets Supportive, dialysis Treat cause

2.12 TTP Details

Feature Details
Pentad MAHA + thrombocytopenia + neurologic signs (triad) + fever + renal dysfunction
Also called Moschcowitz syndrome
Prodrome ~Half have a viral-like illness
Types Single acute episode ยท recurrent (11โ€“28%) ยท drug-induced (ticlopidine ~0.025%, clopidogrel 4ร— less) ยท chronic relapsing (from infancy)
Hemolysis labs Hb <10 g/dL, โ†“ haptoglobin, hemoglobinuria, hemosiderinuria, โ†‘ indirect bilirubin, โ†‘ LDH, polychromasia
Marrow Erythroid hyperplasia; normal/โ†‘ megakaryocytes
ADAMTS-13 Cleaves ULVWF (made by endothelium, Weibel-Palade bodies); acts better under high shear
ULVWF Present early; disappear as episode progresses (consumed); presence in remission predicts relapse (90%)
Refractory (no response in 5 days) Vincristine, azathioprine, splenectomy, staphylococcal protein A column
Outcome >80% fatal before 1990; ~80% survive with early plasma exchange

2.13 Distribution & Dilution

Feature Details
Normal spleen Holds ~1/3 of platelet mass
Splenomegaly Gaucher, Hodgkin, sarcoidosis, lymphoma, cirrhosis, portal hypertension โ€” total mass normal, circulating count โ†“
Hypothermia <25 ยฐC (cardiac surgery) โ€” transient sequestration + function defect
Extracorporeal circuits Platelet damage/activation in pump
Massive transfusion Stored blood has nonviable platelets โ†’ dilution
Mild causes Chronic renal failure, severe iron deficiency, megaloblastic anemia, decompression sickness, chronic hypoxia

2.14 Reactive Thrombocytosis vs Essential Thrombocythemia

Feature Reactive (Secondary) Essential Thrombocythemia
Count 450,000โ€“800,000/ยตL (occasionally 1โ€“2 million) Rodak: persistently >1 million/ยตL (may reach several million)*
Duration Limited โ€” resolves with cause Persistent
Cause Blood loss, surgery, splenectomy, iron deficiency, inflammation, infection, malignancy, exercise Clonal stem cell MPN
Platelet morphology Normal Giant, bizarre, agranular (pale blue), clumps, megakaryocyte fragments
Function Normal Abnormal โ€” no aggregation with epinephrine, โ†“ ADP, normal collagen
Megakaryocytes Normal morphology, normal/โ†‘ โ†‘ number, large, atypical, clusters
TPO regulation Responsive Autonomous
Thrombosis/bleeding No Thrombosis (main cause of death); mucocutaneous bleeding (GI)

*Current WHO criteria use a threshold of โ‰ฅ450 ร— 10โน/L plus JAK2/CALR/MPL โ€” Rodak’s 1 million/ยตL is older. Check which standard your exam version uses.

2.15 Causes of Reactive Thrombocytosis (Box 40-3)

Feature Details
Hemorrhage/surgery Low 2โ€“6 days โ†’ rebound โ†’ normal in 10โ€“16 days
Postsplenectomy Often >1 million/ยตL; peak 1โ€“3 weeks; elevated 1โ€“3 months (years in chronic anemia)
Iron deficiency ~50% of cases; up to 2 million/ยตL; normal 7โ€“10 days after iron therapy
Inflammation RA, rheumatic fever, osteomyelitis, ulcerative colitis, infection, malignancy (Hodgkin, carcinoma)
Kawasaki disease Infants/young children (Japanese, Korean; boys); fever โ‰ฅ40 ยฐC โ‰ฅ2 weeks unresponsive to antibiotics; subacute phase platelets up to 2 million; coronary aneurysms; treat with antiplatelet agents + immunoglobulin
Exercise Splenic release/hemoconcentration; baseline within 30 min
Rebound Peak 10โ€“17 days after stopping alcohol/methotrexate or treating Bโ‚โ‚‚ deficiency
Other Hemophilia patients, childbirth, tissue necrosis, renal disorders, hemolytic anemia

2.16 Essential Thrombocythemia โ€” Clinical

Feature Details
Patients Middle-aged/older; M = F; not hereditary
Thrombosis 10โ€“20% at diagnosis; microvascular: digital pain, gangrene, erythromelalgia (burning palms/soles; relieved by aspirin); large vessels too
Bleeding Mucocutaneous, GI most frequent; worsened by aspirin; paradoxical clotting + bleeding
Treatment Hydroxyurea, busulfan, melphalan, ยณยฒP; apheresis in emergencies; interferon-ฮฑ (~60% CR, 28% intolerant); anagrelide (inhibits megakaryocyte maturation; 93% response)
Prognosis Low transformation to acute leukemia

3 ยท Visual Memory Hooks

๐Ÿง  Three mechanisms
“Can’t Make, Can’t Keep, Can’t Find” โ€” production, destruction, distribution.
๐Ÿง  Bleeding thresholds
“50 is safe, 10 is scary” (ร— 10ยณ/ยตL).
๐Ÿง  Pseudothrombocytopenia
“Low count? Look at the slide” โ€” clumps and satellites.
๐Ÿง  Platelet size
“Wiskott is Wee; May-Hegglin and Bernard-Soulier are Big”.
๐Ÿง  May-Hegglin
“May has Mighty platelets and blue Dรถhle bodies โ€” Dominant”.
๐Ÿง  TAR
“TAR = Thrombocytopenia, Absent Radius” โ€” forearm bones.
๐Ÿง  Acute ITP
“Kid, Cold, Cured” โ€” child after a viral cold, remits.
๐Ÿง  Chronic ITP
“Woman, Wait, Workup” โ€” adult female, chronic, needs treatment.
๐Ÿง  ITP marrow
“ITP: Increased megakaryocytes, Increased platelet size”.
๐Ÿง  Hapten
“Penicillin Piggybacks on the platelet”.
๐Ÿง  HIT
“Heparin + PF4 = new face; IgG sees it, platelets Fire” โ€” clots, not bleeding.
๐Ÿง  HIT treatment
“Stop Heparin, Start a DTI โ€” no LMWH”.
๐Ÿง  SRA
“Release at low heparin, silence at high heparin = HIT”.
๐Ÿง  NAIT
“Mom lacks 1a, baby bleeds โ€” even the first baby”.
๐Ÿง  PTP
“One week after blood, platelets vanish โ€” multiparous mom, anti-1a”.
๐Ÿง  TTP pentad
“FAT RN” โ€” Fever, Anemia (MAHA), Thrombocytopenia, Renal, Neuro*.
๐Ÿง  TTP enzyme
“ADAMTS-13 cuts the Giant VWF”.
๐Ÿง  HUS
“Hamburger, Undercooked, Shiga โ€” Kidneys fail”*.
๐Ÿง  TTP vs DIC
“TTP: VWF clots, normal clotting times; DIC: fibrin clots, long clotting times”.
๐Ÿง  HELLP
“Hemolysis, Elevated Liver enzymes, Low Platelets”.
๐Ÿง  ET vs reactive
“Essential ignores Epinephrine”.
๐Ÿง  Postsplenectomy
“Spleen out, platelets over a million”.

*Mnemonic wording is mine; the undercooked-hamburger association is general knowledge, not in the chapter.

Pattern Triggers

If you seeโ€ฆ Thinkโ€ฆ Becauseโ€ฆ
Heparinized burn patient; platelets falling for days but still in range; arterial thrombosis HIT โ†’ stop heparin, PF4โ€“heparin immunoassay/SRA Rodak case*
Low automated count, platelet clumps on EDTA film, no bleeding Pseudothrombocytopenia
Child, petechiae 2 weeks after a viral illness, platelets 15,000, otherwise normal CBC Acute ITP
Woman 30, chronic low platelets, large platelets, โ†‘ marrow megakaryocytes Chronic ITP
Giant platelets + Dรถhle-like neutrophil inclusions, family history May-Hegglin (MYH9)
Boy with eczema, infections, small platelets Wiskott-Aldrich
Newborn without radii, leukemoid reaction TAR syndrome
Healthy mother, first newborn with petechiae and platelets 20,000 NAIT (HPA-1a)
Mother with ITP, newborn count falling over first week Neonatal autoimmune thrombocytopenia
Multiparous woman, severe thrombocytopenia 1 week after RBC transfusion Posttransfusion purpura
Healthy pregnant woman, platelets 125,000 in 3rd trimester Gestational thrombocytopenia
Preeclampsia + hemolysis + โ†‘ AST/ALT + low platelets HELLP
Fever, confusion, schistocytes, low platelets, normal PT/PTT TTP โ†’ plasma exchange
Child with bloody diarrhea then renal failure and schistocytes HUS (E. coli O157:H7)
Schistocytes + โ†“ platelets + โ†‘ PT/PTT + โ†‘โ†‘ D-dimer DIC
Platelets 1,500,000, giant platelets, no epinephrine aggregation Essential thrombocythemia
Platelets 650,000 with microcytic anemia Reactive โ€” iron deficiency
Platelets 1.2 million two weeks after splenectomy Postsplenectomy thrombocytosis
Young child, fever 2 weeks, rash, lymph nodes, platelets 1.5 million Kawasaki disease

*Case answer is my interpretation โ€” the answer key isn’t in the upload.

Commonly Confused Pairs

Feature A B
Acute vs chronic ITP Child, post-viral, <20,000, 90% remit Adult woman, 30โ€“80,000, chronic, GP IIb/IIIa Ab
ITP marrow vs production failure โ†‘ Megakaryocytes โ†“ Megakaryocytes (aplasia, CAMT)
HIT type I vs II Days 1โ€“3, mild, nonimmune 7โ€“14 days (or 1โ€“3 if re-exposed), >30โ€“50% drop, thrombosis
ELISA vs SRA Sensitive, less specific Gold standard, specific, radioactive
NAIT vs neonatal autoimmune Alloantibody; mother’s count normal; severe, ICH 25% Autoantibody; mother has ITP; mild, ICH โ‰ค1%
NAIT vs PTP Fetal platelets destroyed by maternal Ab Recipient’s own platelets destroyed after transfusion
TTP vs HUS Adults, neuro, ADAMTS-13, severe thrombocytopenia Children, renal failure, Shiga toxin, milder
TTP vs DIC Plateletโ€“VWF thrombi; normal PT/PTT, D-dimer Plateletโ€“fibrin thrombi; abnormal coags
Drug-dependent vs hapten Drug promotes Fab binding without covalent link (quinine) Drug + carrier protein = complete antigen (penicillin)
Reactive vs ET Normal function/morphology; temporary Giant platelets; no epinephrine aggregation; persistent
Small vs giant platelets WAS/XLT MYH9, Bernard-Soulier, Paris-Trousseau, gray platelet

Timeline Table

Event Timing Key Point Best Exam Use
Acute ITP onset 1โ€“3 weeks after viral infection Child ITP
Acute ITP recovery ~3 weeks (2โ€“6 weeks) 90% spontaneous ITP
Chronic ITP definition >6 months 10โ€“15% of children ITP
Splenectomy vaccination โ‰ฅ2 weeks before Encapsulated organisms* Therapy
Drug-dependent Ab 1โ€“2 weeks after exposure Quinine Drug ITP
GP IIb/IIIa inhibitors Hours Abciximab Drug ITP
HIT type II 7โ€“14 days (1โ€“3 if prior exposure) Daily counts HIT
Fetal platelet antigens From 14th week of gestation NAIT NAIT
Fetal genotyping / PUBS 10โ€“18 weeks / ~20 weeks Prenatal NAIT NAIT
NAIT recovery 1โ€“2 weeks Maternal Ab decays NAIT
PTP onset ~1 week post-transfusion Anti-HPA-1a PTP
TTP plasma exchange ~5 days before escalation Refractory therapy TTP
Post-hemorrhage count Low 2โ€“6 days; normal 10โ€“16 days Rebound Reactive
Postsplenectomy peak 1โ€“3 weeks; lasts 1โ€“3 months >1 million Reactive
Iron therapy Normal in 7โ€“10 days Iron deficiency Reactive
Rebound thrombocytosis Peak 10โ€“17 days After alcohol/methotrexate Reactive

*Encapsulated-organism rationale is general knowledge.

4 ยท Diagnostic Flowcharts

Flowchart 1 โ€” Rodak case: falling platelets on heparin

Burn patient on UFH (flushes, grafting); platelets dropping steadily for 7 days, still in range โ†’ Calculate % fall from baseline (>30% = suspicious)
New arterial thrombosis; AT, PC, PS, FVL, G20210A, APL normal โ†’ Thrombophilia excluded โ†’ suspect HIT
Stop ALL heparin (flushes too*) โ†’ Start argatroban or bivalirudin
Lab โ†’ PF4โ€“heparin immunoassay โ†’ SRA if needed
Avoid โ†’ LMWH (cross-reacts); platelet transfusion*
โš ๏ธ Common mistake: dismissing HIT because the count is still ‘normal’.

Flowchart 2 โ€” Approach to thrombocytopenia

Low platelet count โ†’ Review blood film
Clumps/satellitism โ†’ Pseudothrombocytopenia โ†’ recollect
True low; other cell lines low or abnormal โ†’ Production defect: marrow (aplasia, leukemia, Bโ‚โ‚‚/folate, drugs, infection)
Isolated; โ†‘ MPV; marrow megakaryocytes โ†‘ โ†’ Destruction: immune (ITP, drug, HIT, NAIT, PTP) or nonimmune (TTP, HUS, DIC, HELLP)
Splenomegaly, hypothermia, massive transfusion โ†’ Distribution/dilution
โš ๏ธ Common mistake: skipping the film and treating a clumping artifact.

Flowchart 3 โ€” Thrombocytopenia with schistocytes

MAHA + low platelets โ†’ PT, PTT, fibrinogen, D-dimer
Abnormal coagulation โ†’ DIC
Normal coagulation + neuro ยฑ fever, adult โ†’ TTP โ†’ ADAMTS-13; plasma exchange now
Normal coagulation + renal failure, child, bloody diarrhea โ†’ HUS โ†’ stool Shiga toxin/culture
Pregnant, hypertension, โ†‘ liver enzymes โ†’ HELLP โ†’ delivery
โš ๏ธ Common mistake: waiting for ADAMTS-13 results before starting plasma exchange.

Flowchart 4 โ€” Neonatal thrombocytopenia

Newborn with petechiae, low platelets โ†’ Check mother’s platelet count and history
Mother normal, HPA-1a negative โ†’ NAIT โ†’ antigen-negative (maternal) platelets ยฑ IVIG; type both parents
Mother has ITP/SLE โ†’ Neonatal autoimmune โ†’ observe; IVIG if bleeding
Sick infant โ†’ Infection (TORCH/CMV), DIC, placental insufficiency
Absent radii / other anomalies โ†’ Inherited (TAR, etc.)
โš ๏ธ Common mistake: assuming a healthy mother rules out an immune cause.

Flowchart 5 โ€” Thrombocytosis

Platelets >450,000/ยตL โ†’ Repeat; look for cause
Recent bleeding, surgery, splenectomy, iron deficiency, inflammation โ†’ Reactive โ€” treat cause
No cause, persistent, >1 million, splenomegaly โ†’ MPN workup (Ch. 19)
Giant bizarre platelets; no epinephrine aggregation โ†’ Supports ET
Thrombosis/erythromelalgia โ†’ Aspirin; cytoreduction (hydroxyurea, anagrelide)
โš ๏ธ Common mistake: labeling every high count as ET without excluding iron deficiency.

*Heparin flush and platelet transfusion cautions are general clinical knowledge.

5 ยท 25 High-Yield Facts

# Fact
1 Thrombocytopenia is the most common cause of clinically significant bleeding.
2 Bleeding is rare with platelets above 50,000/ยตL; risk is high below 10,000/ยตL.
3 Pseudothrombocytopenia from EDTA clumping or satellitism must be excluded by reviewing the film.
4 Thrombocytopenia results from decreased production, increased destruction, or abnormal distribution/dilution.
5 May-Hegglin anomaly is autosomal dominant (MYH9) with giant platelets and Dรถhle-like bodies.
6 Wiskott-Aldrich syndrome is X-linked with small platelets.
7 TAR syndrome is autosomal recessive thrombocytopenia with absent radii.
8 Megaloblastic anemia causes ineffective thrombopoiesis.
9 Acute ITP affects children 1โ€“3 weeks after a viral infection and remits spontaneously in about 90%.
10 Chronic ITP affects adults 20โ€“50, mostly women, with antibodies to GP IIb/IIIa or Ib/IX.
11 ITP shows large platelets and increased marrow megakaryocytes.
12 Chronic ITP needs treatment when platelets fall below 30,000/ยตL.
13 Quinine-type drug-dependent antibodies bind platelet glycoproteins only when the drug is present.
14 Penicillin causes thrombocytopenia by the hapten mechanism.
15 HIT is caused by IgG to heparinโ€“PF4 complexes whose Fc activates platelet FcฮณIIa receptors.
16 A >30% fall from baseline can signal HIT even when the count is within the reference interval.
17 The serotonin release assay is the gold standard for HIT; ELISA is more sensitive but less specific.
18 HIT is treated by stopping heparin and substituting a direct thrombin inhibitor; LMWH cross-reacts.
19 NAIT is most often caused by maternal antibody to HPA-1a and can affect the first pregnancy.
20 Posttransfusion purpura occurs about 1 week after transfusion, usually with anti-HPA-1a, and is treated with IVIG.
21 Gestational thrombocytopenia is the most common cause of thrombocytopenia in pregnancy.
22 TTP is caused by deficient ADAMTS-13, allowing ultra-large VWF multimers to form plateletโ€“VWF thrombi.
23 TTP has normal PT, PTT, fibrinogen and D-dimer, distinguishing it from DIC; it is treated with plasma exchange.
24 Childhood HUS is caused by Shiga toxin from E. coli O157:H7 or Shigella and causes renal failure.
25 Essential thrombocythemia platelets fail to aggregate with epinephrine; reactive thrombocytosis has normal function.
โญ EXAM TIP โ€” The single most testable pattern

Child + post-viral + isolated low platelets โ†’ acute ITP. Heparin + falling count (>30โ€“50%) + clots โ†’ HIT โ†’ stop heparin, give argatroban. Schistocytes + low platelets + normal PT/PTT โ†’ TTP (neuro, adult) or HUS (renal, child). Healthy mother + sick first baby โ†’ NAIT (HPA-1a). No epinephrine aggregation + giant platelets โ†’ ET.

Quick Interpretation Table

Lab Finding Clinical Interpretation
Heparinized patient, platelets 390 โ†’ 230 over 7 days, arterial thrombosis, thrombophilia workup normal HIT โ€” stop heparin, PF4 immunoassay/SRA, argatroban (Rodak case study)*
Platelets 45 on analyzer; film shows large clumps Pseudothrombocytopenia โ€” recollect
Plts 12,000, MPV โ†‘, marrow megakaryocytes โ†‘, 3-year-old Acute ITP
ELISA PF4 positive, SRA negative, 4Ts low Probably nonpathogenic antibody โ€” HIT unlikely
Hb 8, plts 18, schistocytes, LDH โ†‘, PT/PTT normal, confusion TTP
Plts 30, schistocytes, PT/PTT โ†‘, fibrinogen 80, D-dimer โ†‘โ†‘ DIC
Plts 1.4 million, giant platelets, aggregation absent with epinephrine Essential thrombocythemia
Plts 700,000, ferritin low, MCV 70 Reactive thrombocytosis (iron deficiency)

*Illustrative numbers are mine; the case answer is my interpretation.

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 Questions

Answer each question to see a full explanation, why the other options are wrong, and the trap examiners set.

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

Basics

  • Ref 150โ€“450 ร— 10โน/L
  • Bleeding rare >50k; high risk <10k
  • Exclude EDTA clumping/satellitism
  • Production ยท destruction ยท distribution
  • Mucocutaneous bleeding

Inherited

  • WAS: X-linked, small
  • May-Hegglin: MYH9, AD, giant, Dรถhle-like
  • TAR: AR, absent radii
  • CAMT: MPL โ†’ aplasia
  • Bernard-Soulier: giant, GP Ib/IX

ITP

  • Acute: child, post-viral, 90% remit
  • Chronic: woman 20โ€“50, GP IIb/IIIa Ab
  • โ†‘ MPV, โ†‘ megakaryocytes
  • Treat <30k: prednisone, IVIG, anti-D
  • Splenectomy; vaccinate โ‰ฅ2 wk

Drug-Induced

  • Quinine: drug-dependent Ab
  • Penicillin: hapten
  • Gold, procainamide: autoantibody
  • Abciximab: hours
  • Stop drug; IVIG

HIT

  • IgG vs heparinโ€“PF4; FcฮณIIa
  • 7โ€“14 d (1โ€“3 if re-exposed)
  • >30% fall; rarely <40k; clots
  • SRA gold ยท ELISA sensitive
  • Stop heparin โ†’ argatroban; no LMWH

Neonatal/Transfusion

  • NAIT: HPA-1a, first baby, ICH 25%
  • Rx: antigen-negative maternal plts
  • Neonatal autoimmune: maternal ITP, mild
  • PTP: 1 wk, multiparous, anti-1a, IVIG
  • TORCH/CMV

Pregnancy

  • Gestational: 5%, 100โ€“150k, benign
  • Preeclampsia: 20 wk, HTN + protein
  • HELLP: hemolysis, LFTs, low plts
  • Treat: delivery, MgSOโ‚„
  • TTP may present in pregnancy

TTP / HUS / DIC

  • TTP: ADAMTS-13, ULVWF, pentad
  • TTP: normal PT/PTT โ†’ plasma exchange
  • HUS: child, O157:H7/Shigella, kidneys
  • DIC: fibrin thrombi, โ†‘ PT/PTT, D-dimer
  • Ticlopidine/clopidogrel TTP

Distribution

  • Spleen holds 1/3
  • Splenomegaly โ†’ sequestration
  • Hypothermia <25 ยฐC
  • Massive transfusion dilution
  • Bypass circuits

Thrombocytosis

  • >450k; reactive โ‰ค800k
  • Splenectomy >1M; iron deficiency 50%
  • Kawasaki, rebound, exercise
  • ET: giant plts, no epinephrine response
  • ET: thrombosis, erythromelalgia; anagrelide

9 ยท Final Memory Map

  • ๐Ÿฉธ THROMBOCYTOPENIA & THROMBOCYTOSIS
    • Thrombocytopenia Basics
      • Reference, bleeding thresholds, skin lesions
      • Pseudothrombocytopenia
    • Decreased Production
      • Inherited: WAS, MYH9, TAR, CAMT, BSS
      • Neonatal, drugs, viruses, megaloblastic, marrow replacement
    • Immune Destruction
      • ITP acute vs chronic
      • Drug-induced: dependent, hapten, autoantibody
      • HIT
      • NAIT ยท neonatal autoimmune ยท PTP
      • Secondary: interferon, CLL, SLE, malaria
    • Nonimmune Destruction
      • Pregnancy: gestational, preeclampsia, HELLP
      • TTP ยท HUS ยท DIC
      • Direct drugs: ristocetin, protamine
    • Distribution/Dilution
      • Spleen ยท hypothermia ยท bypass ยท massive transfusion
    • Thrombocytosis
      • Reactive: bleeding, splenectomy, iron deficiency, inflammation, Kawasaki, rebound
      • MPN: ET, PV, CML, PMF



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