What are the typical Complete Blood Count (CBC) results in a patient with dengue?

Typical CBC Results in Dengue Fever

Thrombocytopenia and leukopenia are the hallmark hematological findings in dengue fever, with thrombocytopenia occurring in 70-90% of patients and leukopenia in 76% of cases. 1, 2, 3

Core Hematological Findings

Platelet Count

• Thrombocytopenia (platelet count <150,000/mm³) is present in 70-90% of dengue patients, making it the most consistent CBC abnormality 1, 2, 3
• Platelets typically reach their nadir at days 5-7 after fever onset, with counts often dropping to 20,000-50,000/mm³ 4
• The lowest recorded platelet counts in dengue series range from 26,000 to 87,000/mm³ 2, 4
• Thrombocytopenia <100,000/mm³, particularly when declining rapidly, indicates need for hospitalization and close monitoring 1

White Blood Cell Count

• Leukopenia (WBC <4,000/mm³) occurs in 64-76% of dengue patients 2, 4, 3
• The WBC nadir typically occurs at days 5-6 after fever onset, with counts dropping as low as 1,000-2,000/mm³ 4
• Leukopenia shows significant association with disease severity (p=0.001) 2

Differential Count Characteristics

• Relative lymphocytosis with atypical lymphocytes and plasmacytoid cells is a consistent finding at presentation 5
• Higher lymphocyte percentage at admission predicts shorter hospital stay (p=0.028), with higher percentages correlating with faster recovery 3
• The differential shifts from relative lymphocytosis toward normalization as symptoms improve 5

Hemoglobin and Hematocrit

• Raised hematocrit is a consistent finding, reflecting plasma leakage and hemoconcentration 5
• Rising hematocrit (>20% increase from baseline) is a warning sign requiring hospitalization 1
• Typical hemoglobin values during illness average 13.2 ± 1.9 g/dL 4

Temporal Pattern of CBC Changes

The CBC abnormalities follow a predictable timeline:

• Days 1-4: Progressive decline in WBC and platelets begins 4
• Days 5-7: Both parameters reach their nadir; this is the critical phase when plasma leakage and bleeding risk are highest 1, 4
• Post-day 7: Recovery begins, with normalization occurring over subsequent days 4, 5

Clinical Correlation with Disease Severity

Both leukopenia and thrombocytopenia show significant association with dengue severity (p<0.001 for thrombocytopenia, p=0.001 for leukopenia) 2. These parameters help distinguish:

• Dengue without warning signs: Mild thrombocytopenia and leukopenia may be present 1, 2
• Dengue with warning signs: More pronounced cytopenias, particularly platelets <100,000/mm³ 1, 2
• Severe dengue/DHF: Marked thrombocytopenia (often <50,000/mm³), significant leukopenia, and elevated hematocrit 2, 5

Bone Marrow Findings (When Performed)

• Mild hypocellularity in the acute stage (<1 week) with return to normal cellularity in convalescence 4
• Increased megakaryocytes with various stages of maturation, suggesting peripheral platelet destruction rather than production failure 4
• CFU-GM shows no growth or low colony count within one week, suggesting virus-induced destruction or inhibition of myeloid progenitor cells 4

Key Clinical Pitfalls

Do not rely on platelet count alone to determine bleeding risk—prophylactic platelet transfusion in dengue does not reduce clinical bleeding and may actually increase bleeding risk in patients with poor platelet recovery 6. The absence of thrombocytopenia significantly reduces the probability of dengue (negative likelihood ratio 0.2-0.45), making it a useful rule-out finding 7.

Monitor CBC daily during the critical phase (days 4-7) to track platelet counts and hematocrit levels, as these parameters guide fluid management and identify progression to severe disease 1, 2.