Does dengue infection affect the White Blood Cell (WBC) count?

Impact of Dengue Infection on White Blood Cell Count

Dengue infection typically causes leukopenia (low white blood cell count), which is a characteristic laboratory finding that can help distinguish dengue from other febrile illnesses. This hematological change is an important diagnostic marker and can indicate disease progression.

Hematological Changes in Dengue

White Blood Cell Changes

• Leukopenia (<4,000 cells/mm³) is present in approximately 65-76% of dengue patients 1, 2
• WBC typically reaches its lowest point (1,000-2,000/mm³) around the 5th-6th day after fever onset 2
• Leukopenia can be detected from day 1 to day 10 of illness 3
• The mechanism appears to involve virus-induced destruction or inhibition of myeloid progenitor cells 2

Differential White Blood Cell Changes

• Lymphocyte pattern changes: The neutrophil to lymphocyte ratio is typically >1 during the first 5 days of illness, then reverses (becomes <1) on days 6-9 3
• Increased monocytes: Higher monocyte counts are seen on days 1-4 of illness 3
• Increased atypical lymphocytes: Higher percentage observed on days 5-9 3
• Increased eosinophils: Higher percentage noted on days 9-10 3

Other Associated Hematological Findings

Thrombocytopenia

• Occurs in 40-54% of dengue patients 1, 2
• Platelet count typically reaches its lowest point (20,000-50,000/mm³) around days 5-7 after fever onset 2
• Often coincides with leukopenia
• May be caused by TNF-α-induced thrombophagocytosis by monocytes 4

Hemoconcentration

• Higher hemoglobin and hematocrit levels from day 3 to day 10 of illness 3
• Reflects plasma leakage, a key feature of severe dengue

Clinical Significance

Diagnostic Value

• The combination of leukopenia and a positive tourniquet test correctly identifies 94% of dengue patients 5
• Absence of leukopenia combined with a negative tourniquet test may be useful to rule out dengue 5
• Leukopenia and thrombocytopenia show significant association with the severity of dengue infection 1

Disease Monitoring

• Monitoring WBC and platelet counts is crucial for identifying progression to severe disease
• The severity of dengue infection shows significant association with leukopenia (p=0.001) and thrombocytopenia (p<0.001) 1
• The critical phase of dengue often coincides with defervescence (fever reduction) and is when severe manifestations typically appear 1

Clinical Application

When evaluating a patient with acute febrile illness in an endemic area or with relevant travel history:

1. Obtain a complete blood count with differential

2. Look specifically for:

   • WBC <4,000 cells/mm³
   • Platelet count <150,000 cells/mm³
   • Reversal of neutrophil:lymphocyte ratio after day 5
   • Hemoconcentration (rising hematocrit)

3. Monitor these parameters daily during the acute phase of illness

4. Be vigilant for warning signs of severe dengue when leukopenia and thrombocytopenia are present

Pitfalls and Caveats

• Leukopenia is not specific to dengue and can occur in other viral infections
• During concurrent outbreaks (e.g., dengue and influenza), the specificity of these hematological markers decreases 5
• The timing of blood sampling relative to fever onset is crucial for proper interpretation
• Baseline hematological values may vary by population and individual factors

In summary, leukopenia is a characteristic finding in dengue infection that, when combined with other clinical and laboratory features, can aid in diagnosis and monitoring disease progression. The presence of both leukopenia and thrombocytopenia should raise suspicion for dengue in the appropriate clinical context.