CBC Reviewer (HY)

HIGH-YIELD CBC EXAM REVIEWER

MLS 417-LAB | Hematology

CBC BASICS — MUST KNOW

• Most commonly ordered lab test

• Comprises RBC, WBC, Platelets

• Done via automated analyzer; manual = only for suspicious/critical results

• Phase 1 = Translate numbers → medical terms

• Phase 2 = Recognize disease patterns

• Delta Check = compare patient's current vs. own previous results (best comparison, not just reference interval)

WBC — HIGH YIELD POINTS

Terminology (MEMORIZE)

WBC Count Interpretation

• ↑ WBC = Leukocytosis

• ↓ WBC = Leukopenia

• Relative count = percentage (%)

• Absolute count = Relative % × Total WBC count

• Always use absolute counts for accurate interpretation — relative counts can be misleading!

Left Shift — HIGH YIELD

• Presence of band cells or younger in peripheral blood

• Indicates infection (most common cause)

• Origin: Josef Arneth (1920s) — Arneth Count / Arneth-Schilling Count

• Fewer neutrophil segments → farther LEFT on graph → Left Shift

Immature WBC Rules

WBC Morphology Abnormalities

• Toxic granulation → Lead poisoning / severe infection

• Hypersegmentation → Megaloblastic anemia (>5 lobes)

• Automated analyzers cannot always detect morphologic abnormalities → manual review needed

NRBC Correction Formula — MUST KNOW

$\text{Corrected WBC}=\frac{\text{Observed WBC}\times100}{100+\text{\# NRBC}}$

RBC — HIGH YIELD POINTS

RBC Indices Formulas — MEMORIZE

MCHC = HGB ÷ HCT × 100
MCH = HGB ÷ RBC × 10
MCV = HCT ÷ RBC × 10

Rule of Three — HIGH YIELD

HCT = HGB × 3

• Rule of three fails → analytical error (falsely ↑ or ↓ HGB or HCT)

Step 1: Anemia vs Polycythemia

• Use HGB (more reliable) — direct measure of O₂-carrying capacity

• HCT = influenced by plasma volume (e.g., dehydration → falsely ↑ HCT)

Step 2: MCV — Cell Size Classification

TAILS — Microcytic Anemia Mnemonic

Macrocytic — HIGH YIELD FACTS

• Megaloblastic anemia → Folate & Vitamin B12 deficiency

• VitB12 deficiency → Diphyllobothrium latum (fish tapeworm)

• VitB12 malabsorption → Fasciolopsis buski

• Morphology: hypersegmented neutrophils + macrocytes + oval macrocytes

Step 3: MCHC — Hemoglobin Content

• ↑ MCHC = Spherocytosis OR analytical/lab error

• MCHC is best used as internal quality control

Step 4: RDW — Size Variation

• Measures anisocytosis (variation in RBC volume)

• Reference interval: 11.5–14.5%

• ↑ RDW = anisocytosis present

• Only increased RDW is clinically significant

• Reported as CV or SD

• Same MCV doesn't mean same size distribution

• MCV = average; RDW = variation

Step 5: Reticulocyte Count

• NOT a standard part of CBC (ordered separately, same analyzer)

• Assesses bone marrow erythropoietic activity

• Anemia + ↓ retic count → BM failure (investigate!)

• IRF (Immature Reticulocyte Fraction) = sensitive BM activity marker

Step 6: RBC Morphology

• Only report when abnormalities are present

• Anemia present → Wright-stained peripheral blood film MUST be reviewed

• Blood film = quality control (must match analyzer results)

• Abnormalities to note: size, shape, color, arrangement, inclusions, immature RBCs

Step 7: RBC Count & MCH

• RBC count NOT used to judge anemia alone

  • Thalassemia = low HGB but normal or HIGH RBC count

• Parameters for anemia = HCT + HGB + Morphology

• MCH follows MCV (small cells = less Hgb; large cells = more Hgb)

• MCH is the least clinically useful index when other parameters are available

PLATELET — HIGH YIELD POINTS

Platelet Parameters

• ↑ Platelets = Thrombocytosis

• ↓ Platelets = Thrombocytopenia → unexplained bruising/bleeding

Platelet Count + WBC + HGB Assessment

MPV Interpretation

• MPV = counterpart of MCV (measures average platelet size)

• ↑ MPV = larger platelets on PBS

• Must correlate MPV with platelet diameter on peripheral blood smear

Platelet Morphology Terms

QUICK PATTERN RECOGNITION TABLE

HIGHEST YIELD FACTS — LAST MINUTE REVIEW

You got this! Focus on formulas, TAILS, patterns, and terminology!