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Quick Reference
  • Neutrophils: 40-70% (1,500-7,000/μL) - bacterial infection fighters
  • Lymphocytes: 20-40% (1,000-4,000/μL) - viral infection and adaptive immunity
  • Monocytes: 2-8% (200-800/μL) - phagocytes and antigen presenters
  • Eosinophils: 1-4% (50-400/μL) - parasites and allergic reactions
  • Basophils: 0.5-1% (20-100/μL) - allergic and inflammatory responses
  • Critical Value: Absolute neutrophil count (ANC) <500/μL (neutropenic fever risk)
  • Primary Use: Differentiate infection types, diagnose immune disorders, monitor chemotherapy
  • Sample Type: Whole blood (EDTA tube - purple top)
  • Key Point: Absolute counts matter more than percentages; calculate ANC for neutropenia assessment

Test Description

What is the WBC Differential?

The WBC differential breaks down the total white blood cell count into the five major types of leukocytes, reported as both percentages and absolute counts. This reveals which specific cell type is elevated or decreased, providing crucial diagnostic information that the total WBC count alone cannot provide.

Why Differential Matters More Than Total WBC

The total WBC count tells you HOW MANY white cells are present, but the differential tells you WHICH TYPES are abnormal. This distinction is critical:

  • WBC 15,000 with 90% neutrophils (13,500 neutrophils): Suggests bacterial infection
  • WBC 15,000 with 80% lymphocytes (12,000 lymphocytes): Suggests viral infection or CLL
  • WBC 15,000 with 30% eosinophils (4,500 eosinophils): Suggests parasitic infection or allergic reaction
Percentages vs. Absolute Counts: Always look at absolute counts, not just percentages. A "low percentage" of neutrophils may still represent a normal absolute count if total WBC is high. Conversely, a "normal percentage" may represent severe neutropenia if total WBC is low. Calculate absolute count: (WBC × percentage) ÷ 100.

The Five Types of White Blood Cells

Each WBC type has distinct functions and clinical significance when elevated or decreased.

Normal Ranges

WBC differential values are reported as both percentages of total WBC and absolute counts. Both are important for clinical interpretation.

Swipe to see more
Cell Type Normal % of WBC Absolute Count (/μL) Primary Function
Neutrophils (total) 40-70% 1,500-7,000 Bacterial infection defense
  Segmented (mature) 40-60% 1,800-7,000 Fully mature neutrophils
  Bands (immature) 0-5% 0-500 Young neutrophils (left shift)
Lymphocytes 20-40% 1,000-4,000 Viral immunity, adaptive immunity
Monocytes 2-8% 200-800 Phagocytosis, antigen presentation
Eosinophils 1-4% 50-400 Parasites, allergic responses
Basophils 0.5-1% 20-100 Allergic and inflammatory responses
Important Considerations:
  • Absolute neutrophil count (ANC): ANC = WBC × (% neutrophils + % bands) ÷ 100. ANC <500/μL is medical emergency (neutropenic fever risk)
  • Automated vs manual differential: Automated analyzers flag abnormalities requiring manual review by technologist
  • Age variations: Children normally have higher lymphocyte percentages than adults ("lymphocyte predominance" until age 4-6)
  • Ethnic variations: Benign ethnic neutropenia common in African, Middle Eastern populations (baseline ANC 1,000-1,500)
Interpretation Guidelines

Common Differential Patterns

Bacterial Infection Pattern:
  • Neutrophilia (often >70-80%)
  • Left shift (bands >5%)
  • Total WBC elevated (often 12,000-20,000)
  • Example: WBC 18,000, neutrophils 85% (15,300), bands 10% (1,800), lymphocytes 10% (1,800)
Viral Infection Pattern:
  • Lymphocytosis (often >40-50%)
  • Atypical lymphocytes (in EBV, CMV)
  • Relative neutropenia (percentage decreased)
  • Example: WBC 12,000, neutrophils 30% (3,600), lymphocytes 60% (7,200), 15% atypical lymphocytes
Parasitic Infection Pattern:
  • Eosinophilia (often >10-20%)
  • Total WBC normal or mildly elevated
  • Example: WBC 10,000, neutrophils 50% (5,000), eosinophils 20% (2,000), lymphocytes 25% (2,500)
Leukemia Pattern:
  • Markedly abnormal differential (e.g., 80% blasts, persistent lymphocytosis >5,000)
  • Total WBC may be low, normal, or extremely high
  • Often with anemia and/or thrombocytopenia
  • CML example: WBC 80,000, neutrophils 60% (48,000), myelocytes 10%, metamyelocytes 8%, basophils 5%
  • CLL example: WBC 40,000, lymphocytes 90% (36,000), mature-appearing, smudge cells

Calculating Absolute Counts

Always calculate absolute counts from percentages to assess true cell numbers:

  • Formula: Absolute count = (Total WBC × percentage) ÷ 100
  • Example 1: WBC 4,000, neutrophils 30% → ANC = (4,000 × 30) ÷ 100 = 1,200/μL (mild neutropenia)
  • Example 2: WBC 20,000, neutrophils 30% → ANC = (20,000 × 30) ÷ 100 = 6,000/μL (normal absolute count despite low percentage)
Clinical Pearl
Relative vs. Absolute Changes: A patient with bacterial infection may have high neutrophil percentage (75%) but normal absolute neutrophil count if total WBC is low. Conversely, a patient on steroids may have low lymphocyte percentage (10%) but normal absolute lymphocyte count if total WBC is high. Always calculate absolute counts.
Interfering Factors

Medications Affecting Differential

  • Corticosteroids: Increase neutrophils (demargination), decrease lymphocytes and eosinophils
  • G-CSF/GM-CSF: Increase neutrophils markedly
  • Chemotherapy: Decrease all cell lines, especially neutrophils
  • Epinephrine: Increase neutrophils and lymphocytes (demargination)

Physiologic Variations

  • Age: Children have higher lymphocyte percentages than adults (50-60% normal until age 4-6)
  • Exercise: Transient neutrophilia and lymphocytosis
  • Pregnancy: Mild neutrophilia, especially during labor
  • Smoking: Chronic mild neutrophilia
  • Time of day: Diurnal variation in WBC counts

Pre-analytical Errors

  • Sample storage: WBCs degrade over time; analyze within 4 hours
  • Automated flags: Abnormal cells trigger manual review by technologist
  • Interfering substances: Nucleated RBCs can be counted as WBCs, falsely elevating count
Clinical Pearls
Clinical Pearl
"Neutrophils = bacteria, lymphocytes = viruses": This oversimplification is generally true. Neutrophilia with left shift strongly suggests bacterial infection. Lymphocytosis with atypical lymphocytes suggests viral infection (especially EBV, CMV).
Clinical Pearl
Always calculate absolute counts: A "low percentage" doesn't mean low absolute count if total WBC is high. Calculate ANC, absolute lymphocyte count, absolute eosinophil count to assess true values. Percentages can be misleading.
ANC <500 is neutropenic fever emergency: Fever in patient with absolute neutrophil count <500/μL requires immediate broad-spectrum antibiotics without waiting for cultures. This is life-threatening immunosuppression with high risk of bacterial sepsis and fungal infections.
Clinical Pearl
Left shift indicates acute stress: Bands >5% or presence of more immature forms (metamyelocytes, myelocytes) indicates bone marrow releasing young neutrophils in response to acute bacterial infection or severe inflammation. This supports diagnosis of bacterial infection even if total WBC is normal.
Atypical lymphocytes = viral infection: Reactive lymphocytes with enlarged, irregular cytoplasm. >10% atypical lymphocytes strongly suggests infectious mononucleosis (EBV), CMV, or other viral infections. Order monospot or EBV serology to confirm.
Clinical Pearl
Eosinophilia = think parasites, allergies, drugs: In developed countries, most eosinophilia is due to allergies (asthma, atopic dermatitis) or medications. In developing countries or travelers, think parasitic infections (helminths). Severe eosinophilia (>5,000) risks end-organ damage.
Basophilia is a red flag: Basophils are normally <1%. Basophilia (>1-2%) is uncommon and often signals myeloproliferative disorder, especially chronic myeloid leukemia (CML). If basophils elevated, refer to hematology for BCR-ABL testing.
Clinical Pearl
Steroid effect on differential: Corticosteroids cause neutrophilia (demargination) and lymphopenia within hours. This can mask infection. If patient on steroids has "normal" WBC, consider that it may be falsely reassuring. Look at clinical picture and inflammatory markers (CRP, procalcitonin).
Benign ethnic neutropenia: African, Middle Eastern, and West Indian populations often have baseline neutrophil counts of 1,000-1,500 without increased infection risk. This is normal genetic variant. Document as "benign ethnic neutropenia" to avoid repeated unnecessary workups.
Clinical Pearl
Monocytosis in recovery: After chemotherapy or acute infection, monocytes return to normal first (before neutrophils). Monocytosis during recovery is reassuring sign of bone marrow regeneration.
References
  1. Kratz, A., Ferraro, M., Sluss, P. M., & Lewandrowski, K. B. (2004). Laboratory reference values. New England Journal of Medicine, 351, 1548-1564.
  2. Lee, M. (Ed.). (2009). Basic skills in interpreting laboratory data. Ashp.
  3. Farinde, A. (2021). Lab values, normal adult: Laboratory reference ranges in healthy adults. Medscape. https://emedicine.medscape.com/article/2172316-overview?form=fpf
  4. Nickson, C. (n.d.). Critical Care Compendium. Life in the Fast Lane • LITFL. https://litfl.com/ccc-critical-care-compendium/
  5. Farkas, Josh MD. (2015). Table of Contents - EMCrit Project. EMCrit Project. https://emcrit.org/ibcc/toc/
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