CBC and Platelet Findings in Typhoid Fever
Typhoid fever typically presents with leucopenia (particularly absolute neutropenia with relative lymphocytosis), thrombocytopenia, anemia, and eosinopenia on complete blood count.
Key Hematological Findings
White Blood Cell Count
- Normal to low WBC count (5,000-9,000 cells/mm³) is characteristic 1
- Leucopenia with absolute neutropenia and relative lymphocytosis is highly suggestive of typhoid fever when present 2
- A WBC count >10,000 cells/mm³ provides strong presumptive evidence against typhoid fever (odds ratio 0.03) 2
- Leucopenia was found in 31% of cases in one study, while paradoxically leucocytosis occurred in 16% 3
Platelet Count
- Thrombocytopenia is common 4, 5
- Abnormal platelet counts occurred in 19% of pediatric cases 3
- Decreased mean platelet volume (MPV) was the most common finding (31% of cases) and may serve as an early diagnostic clue 3
Hemoglobin/Hematocrit
- Anemia is frequently present 4, 5
- Anemia occurred in 16% of pediatric cases 3
- Most cases maintain normal hematocrit values, though significant reductions in PCV and hemoglobin concentration have been documented 4
Other Findings
- Eosinopenia is common (20% of cases) 3, 5
- Eosinophilia may paradoxically occur in 12% of cases 3
- Bone marrow examination shows myeloid maturation arrest, decreased erythroblasts and megakaryocytes, with increased phagocytic activity of histiocytes 5
Important Clinical Context
The guideline emphasizes that full blood count may be normal or deranged in almost any pattern 6, making CBC findings non-specific for diagnosis. However, when leucopenia with absolute neutropenia and relative lymphocytosis is present, it carries an odds ratio of 11.8 for typhoid fever 2.
Common Pitfalls
- Do not rely solely on CBC findings for diagnosis—blood culture remains the reference standard 6, 7
- Normal CBC does not exclude typhoid fever
- The presence of leucocytosis should prompt consideration of alternative diagnoses or complications
Underlying Mechanisms
The hematological changes result from bone marrow suppression, hemophagocytosis, and subclinical disseminated intravascular coagulation 4, 5, explaining the constellation of cytopenias observed.