Master blood film preparation, staining, and systematic examination of peripheral blood smear for ASCP BOC.
ASCPprep.com | Hematology & Hemostasis
Chapter 28 — PERIPHERAL BLOOD FILM EXAMINATION & CBC CORRELATION
ASCP Board Exam · Lab-Focused Study Guide
EDTA Specimens · Platelet Satellitism & Clumping (Pseudothrombocytopenia/Pseudoleukocytosis) · Citrate Correction ×1.1 · Wedge Film Technique & Errors · Wright Staining & Troubleshooting · 10×/40×/50×/100× Examination · WBC & Platelet Estimates · Differential Count · Systematic CBC Summary (WBC, RBC, Platelets) · Practice Questions
1 · Priority Table & Quick Foundation
| Topic | Priority | Why It’s Tested |
|---|---|---|
| WBC estimate (×2000 at 40×, ×3000 at 50×) and platelet estimate (×20,000; RBC-corrected formula) | HIGH | Calculation questions (Rodak Q4, Q5, Q6) |
| EDTA pseudothrombocytopenia/pseudoleukocytosis → citrate recollection, ×1.1 | HIGH | Case study; Rodak Q8 |
| Staining troubleshooting: too alkaline vs too acidic (Box 16-1) | HIGH | Rodak Q2 |
| Wedge film technique: angle, drop size, well-made film, errors | HIGH | Rodak Q1 |
| Absolute counts (% × WBC) and relative vs absolute terminology | HIGH | Rodak Q7 |
| Systematic CBC summary: Hb → MCV → MCHC → RDW → morphology; platelets; Wintrobe terms | HIGH | Rodak Q10, case |
| Optimal area for differential; battlement pattern; 200/300–400 cell counts | MEDIUM | Rodak Q9 |
| Macroscopic clues: blue (proteins/rouleaux), grainy (agglutination), holes (lipids) | MEDIUM | Rodak Q3 |
| Rule of three; MCHC >36 (spherocytes) vs interference | MEDIUM | Instrument QC |
| Bands grouped with neutrophils (CLSI); left shift | MEDIUM | Differential conventions |
| Stain chemistry: eosin vs methylene blue, pH 6.4–6.8 | MEDIUM | Principles |
| Automated slide makers/stainers, CellaVision | LOW | Awareness |
🎯 KEY POINT — Where to spend your time
Focus: the estimate formulas, the EDTA artifacts and citrate fix, the two staining scenarios, wedge-angle corrections, absolute counts and the CBC-summary sequence. Skim: instrument brand names, stainer mechanics, history of the term left shift.
Quick Foundation — from zero
- The CBC (hemogram) counts WBCs, RBCs and platelets, measures hemoglobin and indices; the blood film is its capstone quality check.
- Analyzers are accurate, but some specimens fool them. The film lets you confirm counts (estimates), classify WBCs (differential) and see morphology.
- A good result needs three things: a well-made film (wedge technique), a well-stained film (Wright, correct pH) and a systematic examination (10× → 40/50× → 100×).
- Interpreting the CBC has two phases: phase 1 — summarize the numbers in words (“normocytic normochromic anemia, thrombocytopenia”); phase 2 — recognize the disease pattern (the rest of the book).
💡 Analogy
The analyzer is a speed camera counting cars; the blood film is the traffic officer who actually looks. If platelets travel in clumps (EDTA), the camera counts a bus as one big car — too few platelets and extra “WBCs”. The officer spots it and asks for a different road (citrate tube). A good officer also needs a clear road (well-made film), good lighting (correct stain pH) and a fixed patrol route (systematic exam).
🏥 Why this matters clinically
A falsely low platelet count can trigger needless platelet transfusions or cancelled surgery (the Rodak case is a preoperative patient). A mislabeled or wrong-patient sample is often caught only when the film estimate disagrees with the analyzer. Every lab reports differentials and morphology daily — this chapter is core bench practice.
| Concept | Plain-English Explanation |
|---|---|
| Platelet satellitism | Platelets ring around neutrophils in EDTA → falsely low count |
| Pseudothrombocytopenia | Falsely low platelet count from clumping or satellitism |
| Pseudoleukocytosis | Falsely high WBC count because platelet clumps are counted as WBCs |
| Wedge (push) film | Drop spread by a spreader slide at 30–45° |
| Feather edge | Thin end of the film; checked for clumps and large cells |
| Romanowsky stain | Wright or Wright-Giemsa: eosin + methylene blue |
| Relative count | Percentage of each WBC type |
| Absolute count | % × total WBC = cells × 10⁹/L |
| Left shift | Increased bands or younger neutrophilic cells in blood |
2 · Core Content Tables
2.1 Specimens for Blood Films
| Feature | Details |
|---|---|
| Routine | Lavender/purple-top EDTA (disodium or tripotassium; liquid K₃EDTA mixes more easily) — chelates calcium |
| Timing | Make films within 2–3 h; >5 h at room temperature → echinocytes, spherocytes, necrobiotic leukocytes, vacuolated neutrophils |
| Monocyte vacuoles | Appear almost immediately in EDTA — no evaluation problem |
| EDTA advantages | Many films possible; prevents platelet clumping on the slide (better estimate) |
| Anticoagulant-free | Purists’ choice for morphology; fingerstick/heel-stick films made at bedside |
| Fingerstick limits | Some platelet clumping expected; only a few films before bleeding stops; EDTA microcollection tubes solve both |
2.2 EDTA-Induced Artifacts
| Artifact | Mechanism | Effect on CBC | Film Finding |
|---|---|---|---|
| Platelet satellitism | Platelets surround/adhere to neutrophils | Pseudothrombocytopenia | Platelet rosettes around neutrophils |
| Platelet clumping | Platelet-specific autoantibodies reacting best at room temperature | Pseudothrombocytopenia + pseudoleukocytosis (clumps counted as WBCs); low MPV* | Platelet clumps, often at feather edge |
| Correction | Recollect in sodium citrate (light blue), 9:1 ratio, full tube | Multiply WBC and platelets by 1.1 | Report other parameters from the EDTA tube |
*Low MPV with clumping is inferred from the case study (MPV 6.6 fL), not stated as a rule. 1.1 = 10/9 because blood is 9/10 of the tube (2.7 mL blood + 0.3 mL citrate).
2.3 Manual Wedge Technique
| Feature | Details |
|---|---|
| Slides | 3 × 1 inch (75 × 25 mm), clean; beveled/chamfered edges |
| Drop | ~2–3 mm diameter at one end (too large → long/thick; too small → short/thin) |
| Angle | 30–45°; draw back into drop, let it spread across the width, push quickly and smoothly |
| High Hct (>60%: polycythemia, newborns) | Lower the angle (~25°) so film isn’t too short and thick |
| Very low Hct | Raise the angle |
| Too slow | Pushes large cells (monocytes, granulocytes) to the edges and feather end |
| Pull film | Spreader pushed into the drop, then pulled — less common |
2.4 Features of a Well-Made Film vs Common Errors (Figure 16-4)
| Well-Made Film | Error Seen | Cause |
|---|---|---|
| 2/3–3/4 of slide length | Jagged/rough feather edge | Chipped or rough spreader |
| Finger-shaped, slightly rounded feather edge (not bullet) | Ridges/bands across film | Hesitation in forward motion |
| Lateral edges visible | Long, thin film | Spreader pushed too quickly (or angle too low*) |
| Smooth, no holes or streaks | Short film | Drop too small |
| Rainbow sheen in feather edge held to light | Narrow film | Drop not spread across the width |
| Whole drop picked up and spread | Holes | Dirt/grease on slide or high lipids |
| Uneven, irregular | Uneven pressure on spreader | |
| Streaked/thick start | Time delay — drop began to dry |
*Angle–length link follows from the Hct rules above; Rodak Q1 answer (increase angle for long thin films) is my interpretation.
2.5 Drying & Water Artifact
| Feature | Details |
|---|---|
| Rule | Dry films as fast as possible (small fan) |
| Don’t | Blow on the slide — breath moisture → echinocytes/water artifact |
| Appearance | Moth-eaten RBCs, sharply demarcated central pallor, refractile shiny blotches, crenation where slide dried slowest |
| Contributors | Humidity; water absorbed into alcohol stain; severe anemia (high plasma:RBC ratio) |
| Prevention | Fast drying, tightly capped stain, fix in anhydrous methanol, stains with 10% methanol |
2.6 Wright Stain Chemistry
| Component | Chemistry | Stains | Color |
|---|---|---|---|
| Methanol | Fixative | Fixes cells to slide | — |
| Methylene blue | Basic dye | Acidic (basophilic) components: RNA, nuclei, basophil granules | Blue/purple |
| Eosin | Acidic dye | Basic (eosinophilic) components: hemoglobin, eosinophil granules | Orange/red |
| Neutrophil granules | Neutral pH | Both dyes | Lilac |
| Buffer | 0.05 M sodium phosphate pH 6.4 or aged distilled water (pH 6.4–6.8) | Staining starts only when buffer is added | — |
2.7 Staining Methods
| Feature | Details |
|---|---|
| Manual | Flood slide; stain 1–3 min (fix); add equal buffer → metallic green sheen (“scum”); ≥3 min; rinse with neutral-pH water; wipe back; dry vertically |
| Manual use | High-WBC (leukemic) films and marrows — time easily lengthened; low-volume labs |
| Automated dip (Midas III) | 5–10 min per batch; can’t add stat slides once started; aqueous working solutions stable only 3–6 h |
| Automated platen (Hema-Tek) | Stat slides any time; stain packs stable ~6 months |
| Automated maker/stainer (Sysmex SP-10) | Adjusts drop, angle and speed to Hct; slide every ~30 s |
| Quick stains | ~1 min; modified Wright; good for clinics; quality a concern |
2.8 Staining Troubleshooting (Box 16-1)
| Feature | Too ALKALINE (most common) | Too ACIDIC |
|---|---|---|
| RBCs | Gray (blue-gray) | Pale or red |
| WBCs | Too dark | Barely visible |
| Eosinophil granules | Gray, not orange | Bright orange/red* |
| Causes | Stain/buffer too alkaline · inadequate rinsing · prolonged staining · heparinized blood | Stain/buffer too acidic · underbuffering (too short) · over-rinsing |
*Bright orange eosinophils in acidic stains comes from Rodak Q2’s wording.
2.9 A Well-Stained Film
| Feature | Details |
|---|---|
| Macroscopic | Pink to purple |
| RBCs | Orange to salmon pink |
| WBC nuclei | Purple to blue |
| Neutrophil cytoplasm | Pink to tan with violet/lilac granules |
| Eosinophils | Bright orange refractile granules |
| Too blue | Old slides (stained after ≥1 week) or ↑ proteins (globulins) |
| Best results | Fresh blood (blood itself buffers the stain) |
2.10 Macroscopic Clues Before the Microscope
| Film Appearance | Suggests | Microscopic Finding |
|---|---|---|
| Bluer than normal | ↑ Proteins (plasma cell myeloma) | Rouleaux |
| Grainy | RBC agglutination | Cold hemagglutinin disease |
| Holes | ↑ Lipids | Recheck CBC for lipemia interference |
| Blue specks at feather edge | Markedly ↑ WBCs or platelets | Leukocytosis/thrombocytosis, clumps |
2.11 Systematic Microscopic Examination
| Objective (Total) | Tasks |
|---|---|
| 10× low power (100×) | Overall quality, color, distribution; check lateral/feather edges — >4× cells at edges = snowplow → remake; fibrin strands → reject specimen; rouleaux/agglutination; large abnormal cells (blasts, reactive lymphs), parasites |
| 40× high-dry (400×) or 50× oil | Select the correct area; WBC estimate; morphology survey (50× oil can do differential for experienced staff) |
| 100× oil (1000×) | Differential (100 WBCs), RBC/WBC/platelet morphology, inclusions (Howell-Jolly, Döhle), platelet estimate, NRBCs per 100 WBCs |
| Optimal area | Between thick area and feather edge; RBCs singly distributed, few touching, central pallor visible; ~200–250 RBCs per oil field |
| Too thin | Holes, RBCs flat and large, no pallor — unacceptable |
| Too thick | RBCs piled (rouleaux-like), WBCs distorted |
| Can’t focus at 100× | Slide is upside down; remove oil and flip |
| Oil | Different viscosities don’t mix — wipe before moving to another microscope |
2.12 Estimates — Formulas
| Estimate | Method | Example |
|---|---|---|
| WBC (40× high-dry) | Average WBCs/field (10 fields) × 2000 | 3/field → 6,000/µL |
| WBC (50× oil) | Average WBCs/field × 3000 | 3/field → 9,000/µL |
| Platelets (100× oil) | Average platelets/field (10 fields) × 20,000 | 12–16/field ≈ 280,000/µL; 20/field → 400,000/µL |
| Platelets — anemia/erythrocytosis | (Average platelets/field × RBC count) ÷ 200 RBCs/field | 7 × 1.25 × 10⁶/µL ÷ 200 ≈ 44,000/µL |
| Validation (Box 16-3) | 30 fresh specimens: instrument count ÷ average/field → average ratio → round | Factors differ by microscope field diameter |
2.13 Performing the Differential
| Feature | Details |
|---|---|
| Pattern | Back-and-forth serpentine “battlement” track; include side margins |
| Number | 100 WBCs; 200 if WBC >40 × 10⁹/L; 300–400 if ≥100 × 10⁹/L |
| Check | Percentages must total 100 |
| Avoid | Buffy-coat smears for differentials (distribution errors); 50-cell counts × 2 |
| Low counts | Buffy coat may be screened for blasts only |
| Morphology reporting | Reactive lymphs as %, % of lymphs, or semiquantitative; toxic granulation “present” or 1+–3+; trend toward simply “present” |
| Automation | CellaVision: locates, images and preclassifies cells; operator verifies |
| RBC morphology | Slight/moderate/marked, 1+–3+ (e.g., 3–6 spherocytes/field = 2+), or “present”; must agree with indices/histogram |
2.14 CBC Summary — Principles
| Feature | Details |
|---|---|
| Phase 1 | Summarize numbers in proper terminology |
| Phase 2 | Recognize the disease pattern |
| Reference intervals | Depend on age and sex (RBC parameters by sex; WBC by age in children) |
| Units | SI 7.2 × 10⁹/L = 7.2 × 10³/µL; Hb 128 g/L = 12.8 g/dL; Hct 0.41 L/L = 41%; mm³ = µL |
| Significance clues | Far outside interval; two or more related parameters outside in the same direction; compare with patient’s own prior results |
2.15 Systematic CBC Approach (Box 16-9)
| Step | White Blood Cells | Red Blood Cells | Platelets |
|---|---|---|---|
| 1 | Ensure accurate WBC count (histogram/scatterplot; correct manual counts for NRBCs) | Hemoglobin first — anemia or polycythemia; rule of three | Platelet count — thrombocytopenia/thrombocytosis; pancytopenia/pancytosis |
| 2 | Compare with reference: leukocytosis/leukopenia | MCV — micro/normo/macrocytic | MPV (6.9–10.2 fL) — platelet size |
| 3 | Relative differential | MCHC — normochromic/hypochromic | Morphology and arrangement |
| 4 | Absolute counts (% × WBC) | RDW — anisocytosis (with histogram) | — |
| 5 | Immature cells (left shift) | Morphology; polychromasia/NRBCs/retics | — |
| 6 | Morphologic abnormalities | RBC count, MCH | — |
2.16 WBC Terminology (Table 16-1)
| Cell | Increase | Decrease |
|---|---|---|
| Neutrophil | Neutrophilia | Neutropenia |
| Eosinophil | Eosinophilia | N/A (interval starts near 0) |
| Basophil | Basophilia | N/A |
| Lymphocyte | Lymphocytosis | Lymphopenia (lymphocytopenia) |
| Monocyte | Monocytosis | Monocytopenia |
2.17 Relative vs Absolute Counts (Table 16-2 & Boxes 16-5 to 16-7)
| Feature | Details |
|---|---|
| Example | WBC 13.6; neutrophils 67% (within 48–70%) → absolute 9.1 × 10⁹/L (>8.2) = absolute neutrophilia → bacterial pattern |
| Lesson | Relative values can all be normal while an absolute count is abnormal |
| Check | Sum of absolute counts ≈ WBC |
| ANC | Absolute neutrophil count — key for neutropenia/neutrophilia |
| Bands (Box 16-5) | Group bands with segs: 65% + 18% = 83% > 80% (70 + 10) → neutrophilia |
| CLSI (Box 16-6) | Count bands and neutrophils together — separate band counts have questionable utility |
| Left shift (Box 16-7) | From Arneth’s 1920s graph of neutrophil lobes — fewer lobes plotted to the left |
| Immature others | Prolymphocytes, lymphoblasts, promonocytes, monoblasts named; young eos/basos = “immature”; eosinophilic metamyelocytes counted as eosinophils |
2.18 RBC Parameters — Interpretation
| Feature | Details |
|---|---|
| Hemoglobin | More reliable than Hct for anemia (Hct affected by RBC size) |
| Rule of three | Hb × 3 ≈ Hct — only when RBCs are normocytic, normochromic |
| MCV (Wintrobe) | <80 fL microcytic · 80–100 normocytic · >100 macrocytic |
| MCHC | Normal = normochromic (pallor ~1/3); low = hypochromic; “hyperchromic” is never used |
| MCHC >36 g/dL | Spherocytes (slight increase) |
| MCHC very high (to 60) | Analytical error — lipemia, icterus, very high WBC falsely raise Hb; MCHC is a good internal QC parameter |
| RDW | CV or SD of RBC volume; only increases matter; e.g., 11.5–14.5% — ↑ = anisocytosis; dimorphic histogram = two populations |
| Morphology | Must match indices; polychromasia and NRBCs = marrow response; retic count better |
| RBC count | Not used to judge anemia — thalassemia has normal/high RBC count with low Hb |
| MCH | Follows MCV; least used |
2.19 Platelet Parameters
| Feature | Details |
|---|---|
| Pancytopenia | Possible acute leukemia or aplastic anemia |
| Pancytosis | Often polycythemia vera |
| MPV | 6.9–10.2 fL (legend 6.8–10.2*); ↑ MPV with platelets ≥6 µm = stress/reticulated platelets (e.g., ITP) |
| MPV limits | Wide CV; platelets swell in EDTA — correlate with film |
| Reticulated platelets | Some analyzers count them with nucleic acid dye (like retics) |
| Size terms | Large = 2× normal; giant = >2× normal (or compare to RBC) |
| Other descriptors | Hypogranular/agranular, bizarre/dysplastic, clumped, satellitism |
*Rodak gives two slightly different MPV intervals in the same chapter; use your lab’s.
3 · Visual Memory Hooks
🧠 EDTA artifacts
“Clumps Cut platelets and Create WBCs” — pseudothrombocytopenia + pseudoleukocytosis.
“Clumps Cut platelets and Create WBCs” — pseudothrombocytopenia + pseudoleukocytosis.
🧠 Satellitism
“Platelets Orbit neutrophils like moons”.
“Platelets Orbit neutrophils like moons”.
🧠 Citrate factor
“Nine parts blood, one part citrate → multiply by 1.1” (WBC and PLT only).
“Nine parts blood, one part citrate → multiply by 1.1” (WBC and PLT only).
🧠 Film timing
“Make it within 3, it’s artifact-free”; after 5 h, echinocytes and spherocytes.
“Make it within 3, it’s artifact-free”; after 5 h, echinocytes and spherocytes.
🧠 Wedge angle
“Thick blood, Tilt down; Thin blood, Tilt up” — high Hct lower angle.
“Thick blood, Tilt down; Thin blood, Tilt up” — high Hct lower angle.
🧠 Stain dyes
“Blue is Basic, loves Acid (RNA); Eosin is Acid, loves Basic (Hb)”.
“Blue is Basic, loves Acid (RNA); Eosin is Acid, loves Basic (Hb)”.
🧠 Alkaline stain
“Alkaline = All Gray, All dark”.
“Alkaline = All Gray, All dark”.
🧠 Acidic stain
“Acid = RBCs Red, WBCs Ramble away (barely visible)”.
“Acid = RBCs Red, WBCs Ramble away (barely visible)”.
🧠 Macroscopic
“Blue = protein (rouleaux), Grainy = agglutinins, Holes = fat”.
“Blue = protein (rouleaux), Grainy = agglutinins, Holes = fat”.
🧠 Objectives
“10 Looks, 40 Counts WBCs, 100 Does the Diff and Platelets”.
“10 Looks, 40 Counts WBCs, 100 Does the Diff and Platelets”.
🧠 WBC estimate
“Forty × Two thousand; Fifty × Three thousand”.
“Forty × Two thousand; Fifty × Three thousand”.
🧠 Platelet estimate
“Each platelet per oil field = 20,000”.
“Each platelet per oil field = 20,000”.
🧠 Snowplow
“More than 4× at the edges — the plow pushed them, remake it”.
“More than 4× at the edges — the plow pushed them, remake it”.
🧠 Fibrin
“Fibrin strands = clotted sample, reject”.
“Fibrin strands = clotted sample, reject”.
🧠 Upside-down slide
“Focus at 10 and 40 but not 100? Flip it”.
“Focus at 10 and 40 but not 100? Flip it”.
🧠 Absolute
“Percent × WBC = the truth”.
“Percent × WBC = the truth”.
🧠 Rule of three
“Hb × 3 = Hct, if the cells are normal”.
“Hb × 3 = Hct, if the cells are normal”.
🧠 MCHC
“Over 36: spheres; over 40: suspect the analyzer”*.
“Over 36: spheres; over 40: suspect the analyzer”*.
🧠 RDW
“RDW only rises — Different sizes”.
“RDW only rises — Different sizes”.
🧠 Anemia
“Judge anemia by Hb, not RBC count — thalassemia fools you”.
“Judge anemia by Hb, not RBC count — thalassemia fools you”.
*The ~40 cut-off is my rule of thumb; Rodak says ‘a more dramatic increase (even 60)’.
Pattern Triggers
| If you see… | Think… | Because… |
|---|---|---|
| Healthy preop patient: WBC 15.8, PLT 34, MPV 6.6, film shows platelet clumps | EDTA pseudothrombocytopenia + pseudoleukocytosis → citrate recollection | Rodak case* |
| Platelets ringed around neutrophils | Platelet satellitism | |
| Long, thin film | Increase spreader angle* | |
| Short, thick film, patient Hct 65% | Lower spreader angle (~25°) | |
| RBCs gray, WBCs very dark, eosinophil granules gray | Stain/buffer too alkaline (or heparin sample) | |
| RBCs red, WBCs barely visible | Stain/buffer too acidic, underbuffered, over-rinsed | |
| Film bluer than normal | Increased proteins → rouleaux (myeloma) | |
| Grainy film | RBC agglutination (cold agglutinin) | |
| Film with holes | Lipemia — check indices | |
| Many cells at feather edge and sides | Snowplow effect → remake | |
| Fibrin strands at 10× | Clotted specimen → recollect | |
| Moth-eaten RBCs, refractile blotches | Water/drying artifact | |
| Estimate disagrees with analyzer | Wrong patient/mislabeled, clumping, or analyzer error | |
| WBC normal % but WBC 13.6 and ANC 9.1 | Absolute neutrophilia | |
| MCHC 45 g/dL with lipemic plasma | Falsely high Hb — interference | |
| Hb 11, RBC 6.0, MCV 62 | Thalassemia pattern — RBC count misleading | |
| MPV high, large platelets, low count | Consumption with marrow compensation (e.g., ITP) |
*Case and angle answers are my interpretation — the answer key isn’t in the upload.
Commonly Confused Pairs
| Feature | A | B |
|---|---|---|
| Satellitism vs clumping | Platelets around neutrophils; low PLT | Platelet aggregates; low PLT + high WBC |
| Too alkaline vs too acidic | Gray RBCs, dark WBCs | Red/pale RBCs, faint WBCs |
| Methylene blue vs eosin | Basic dye → acidic structures (blue) | Acidic dye → basic structures (orange) |
| 40× vs 50× estimate | × 2000 | × 3000 |
| Platelet estimate normal vs anemic | × 20,000 | × RBC count ÷ 200 |
| Relative vs absolute | Percentage | % × WBC (× 10⁹/L) |
| Rouleaux vs agglutination | Stacked coins; ↑ proteins; blue film | Clumps; cold antibody; grainy film |
| Too thin vs too thick area | Flat RBCs, no pallor, holes | Overlapping, piled RBCs |
| Hb vs Hct for anemia | More reliable | Affected by RBC size |
| MCHC ↑ spherocytes vs artifact | Just over 36 | Very high (to 60): lipemia, icterus, WBC |
| Large vs giant platelets | ~2× normal | >2× normal |
Timeline Table
| Event | Timing | Key Point | Best Exam Use |
|---|---|---|---|
| Film from EDTA | Within 2–3 h | Quality morphology | Specimen |
| EDTA artifacts | >5 h at room temperature | Echinocytes, spherocytes, necrobiosis | Specimen rejection |
| Monocyte vacuoles | Almost immediately | No problem | Artifact |
| Manual Wright fixation | 1–3 min | Methanol step | Staining |
| Buffer step | ≥3 min | Metallic sheen | Staining |
| Automated stainer batch | 5–10 min | High volume | Staining |
| Aqueous working stain | Stable 3–6 h | Dip stainers | QC |
| Quick stain | ~1 min | Low volume | Staining |
| Old slides | ≥1 week before staining | Too blue | Troubleshooting |
| Automated film maker | ~30 s/slide | Adjusts to Hct | Automation |
4 · Diagnostic Flowcharts
Flowchart 1 — Rodak case: unexpected leukocytosis and thrombocytopenia
| Healthy 56-year-old, preop: WBC 15.8, PLT 34, MPV 6.6; RBC indices normal | → | Review film |
| Only finding: platelets in clumps | → | Suspect EDTA pseudothrombocytopenia + pseudoleukocytosis |
| Question | → | WBC, PLT (and MPV) counts |
| Action | → | Recollect in sodium citrate (full tube); run WBC and PLT; × 1.1 |
| Report | → | WBC and PLT from citrate; all other parameters from EDTA; summary: normal CBC if corrected values normal* |
| ⚠️ Common mistake: reporting a platelet count of 34 and canceling surgery. | ||
Flowchart 2 — Poor film
| Too long/thin | → | Increase angle, larger drop, push slower* |
| Too short/thick | → | Decrease angle (high Hct), smaller drop |
| Holes | → | Clean slides; check lipemia |
| Snowplow at edges | → | Remake — distribution invalid |
| Fibrin strands | → | Reject specimen |
| ⚠️ Common mistake: doing a differential on a snowplowed film — monocytes and granulocytes are overcounted at the edges. | ||
Flowchart 3 — Poor stain (Box 16-1)
| Everything blue-gray, WBCs dark | → | Too alkaline |
| Fix | → | Check buffer pH (6.4–6.8), rinse longer, shorten stain time; avoid heparin samples |
| Everything red/pale, WBCs faint | → | Too acidic |
| Fix | → | Check pH, lengthen buffering, rinse less |
| Still blue | → | Old slide or high proteins — restain fresh film |
| ⚠️ Common mistake: changing the stain before checking the buffer pH. | ||
Flowchart 4 — Systematic CBC summary
| WBC | → | Accurate? → leukocytosis/leukopenia → relative → absolute → immature → morphology |
| RBC | → | Hb (anemia?) → rule of three → MCV → MCHC → RDW → morphology/retics |
| Platelets | → | Count → MPV → morphology |
| Film vs analyzer disagree | → | Investigate: artifact, interference, mislabel |
| Phase 1 output | → | One sentence, e.g., ‘leukopenia with absolute neutropenia; macrocytic normochromic anemia; thrombocytopenia’ |
| ⚠️ Common mistake: judging a neutrophilia from percentages alone. | ||
*Case and film-correction answers are my interpretation.
5 · 25 High-Yield Facts
| # | Fact |
|---|---|
| 1 | The routine hematology specimen is whole blood in a lavender-top EDTA tube, which chelates calcium. |
| 2 | Films from EDTA blood should be made within 2–3 hours; after 5 hours at room temperature artifacts appear. |
| 3 | EDTA-induced platelet satellitism around neutrophils causes pseudothrombocytopenia. |
| 4 | EDTA-induced platelet clumping causes pseudothrombocytopenia and pseudoleukocytosis. |
| 5 | Recollect in sodium citrate and multiply WBC and platelet counts by 1.1 to correct for dilution. |
| 6 | The wedge film uses a 2–3 mm drop and a spreader angle of 30–45 degrees. |
| 7 | For high hematocrits (>60%), lower the spreader angle; for very low hematocrits, raise it. |
| 8 | A well-made film covers 2/3–3/4 of the slide, has a rounded feather edge, visible lateral edges and a rainbow sheen. |
| 9 | Blowing on a slide causes water artifact and echinocytes; dry films quickly. |
| 10 | Wright stain combines eosin (acidic dye) and methylene blue (basic dye); methanol fixes the cells. |
| 11 | Staining begins only when pH 6.4 buffer is added; a metallic sheen indicates proper mixing. |
| 12 | A stain that is too alkaline makes RBCs gray, WBCs too dark and eosinophil granules gray. |
| 13 | A stain that is too acidic makes RBCs pale or red and WBCs barely visible. |
| 14 | A film that looks bluer than normal suggests increased proteins and rouleaux. |
| 15 | At 10×, more than four times as many cells at the edges than the monolayer means the film must be remade. |
| 16 | Fibrin strands on the film indicate a clotted specimen that must be rejected. |
| 17 | WBC estimate = average WBCs per field × 2000 (40× objective) or × 3000 (50× oil). |
| 18 | Platelet estimate = average platelets per 100× oil field × 20,000. |
| 19 | In anemia or erythrocytosis, platelet estimate = average platelets/field × RBC count ÷ 200. |
| 20 | The differential is done in the area where RBCs barely touch, about 200–250 RBCs per oil field. |
| 21 | Count 200 cells if the WBC exceeds 40 × 10⁹/L and 300–400 cells if it is 100 × 10⁹/L or more. |
| 22 | Absolute count = relative percentage × total WBC count. |
| 23 | The rule of three (Hb × 3 ≈ Hct) holds only for normocytic, normochromic RBCs. |
| 24 | An MCHC above 36 g/dL suggests spherocytes; much higher values suggest lipemia, icterus or very high WBC interference. |
| 25 | Hemoglobin, not the RBC count, is used to judge anemia because thalassemia can have a normal or high RBC count. |
⭐ EXAM TIP — The single most testable pattern
WBC estimate: ×2000 (40×) / ×3000 (50×). Platelet estimate: ×20,000, or × RBC ÷ 200 when anemic. Clumps → low PLT + high WBC → citrate × 1.1. Alkaline = gray/dark; acidic = red/faint. Absolute = % × WBC.
Quick Interpretation Table
| Lab Finding | Clinical Interpretation |
|---|---|
| WBC 15.8, PLT 34, MPV 6.6, otherwise normal; platelet clumps on film | EDTA artifact — recollect in citrate; correct ×1.1 (Rodak case study)* |
| WBCs per 40× field: 8,4,7,5,4,7,8,6,4,6 (avg 5.9) | Estimate 11.8 × 10⁹/L |
| RBC 1.25 × 10¹²/L, 7 platelets per oil field | 7 × 1,250,000 ÷ 200 ≈ 44,000/µL |
| 10 platelets per oil field, normal RBC | ~200,000/µL |
| WBC 9.5, lymphocytes 37% | Absolute lymphocytes 3.5 × 10⁹/L |
| WBC 86.3, Hb 9.7, MCV 87.8, MCHC 33.5, PLT 106 | Leukocytosis, normocytic normochromic anemia, thrombocytopenia |
| WBC 3.2, neutrophils 43%, lymphs 45%, Hb 8.5, MCV 125, RDW 20.6, PLT 115; hypersegmented neutrophils, oval macrocytes | Leukopenia (absolute neutropenia and lymphopenia), macrocytic normochromic anemia with anisocytosis, thrombocytopenia (Box 16-8) |
| Neutrophils 65% + bands 18%, WBC 10.8 | Neutrophilia (83% > 80% combined limit) |
*Case answer is my interpretation.
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📝 Practice Questions
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8 · Rapid Revision Sheet
📖 READ THIS 2 HOURS BEFORE YOUR EXAM
Specimen
- EDTA lavender; films within 2–3 h
- >5 h: echinocytes, spherocytes
- Satellitism → ↓ PLT
- Clumps → ↓ PLT, ↑ WBC
- Citrate 9:1 → × 1.1 (WBC, PLT)
Wedge Film
- Drop 2–3 mm; angle 30–45°
- High Hct → lower angle (~25°)
- 2/3–3/4 length, rainbow edge
- Holes = grease/lipids
- Dry fast; don’t blow
Wright Stain
- Methanol fixes
- Methylene blue (basic) → RNA blue
- Eosin (acidic) → Hb orange
- Buffer pH 6.4; metallic sheen
- Old slides/proteins → too blue
Stain Problems
- Alkaline: gray RBCs, dark WBCs
- Alkaline causes: rinse too little, heparin
- Acidic: red RBCs, faint WBCs
- Acidic causes: underbuffer, over-rinse
- Blue film = rouleaux
Exam Sequence
- 10×: quality, snowplow, fibrin
- 40×/50×: area + WBC estimate
- 100×: diff, morphology, PLT
- 200–250 RBCs/oil field
- Upside down → can’t focus 100×
Estimates
- WBC: ×2000 (40×) · ×3000 (50×)
- PLT: ×20,000
- Anemia: PLT/field × RBC ÷ 200
- Validate factor (30 samples)
- Mismatch → mislabel/artifact
Differential
- Battlement pattern
- 100 cells; 200 if >40; 300–400 if ≥100
- Sum = 100%
- Bands + segs together (CLSI)
- No buffy coat diffs
WBC Summary
- Accurate count (NRBCs)
- Leukocytosis/leukopenia
- Relative → absolute (% × WBC)
- Immature cells (left shift)
- Morphology
RBC Summary
- Hb first; rule of three
- MCV 80–100
- MCHC: hypo; >36 spherocytes
- Very high MCHC = interference
- RDW ↑ = anisocytosis
Platelet Summary
- Count; pancytopenia/pancytosis
- MPV 6.9–10.2 fL
- ↑ MPV + large = consumption
- Large 2× · giant >2×
- Clumps/satellitism noted
9 · Final Memory Map
- 🔬 BLOOD FILM & CBC CORRELATION
- Specimen
- EDTA timing and artifacts
- Satellitism · clumping · citrate × 1.1
- Fingerstick films
- Film Preparation
- Wedge technique, angle, drop
- Well-made features vs errors
- Automated makers · drying artifact
- Staining
- Wright chemistry and buffer pH
- Manual · automated · quick stains
- Alkaline vs acidic troubleshooting
- Examination
- Macroscopic clues
- 10× → 40/50× → 100×
- WBC and platelet estimates
- Differential technique
- CBC Summary
- WBC: count, relative, absolute, immature, morphology
- RBC: Hb, MCV, MCHC, RDW, morphology
- Platelets: count, MPV, morphology
- Specimen