Significance of Total Leukocyte Count (TLC) and Differential Leukocyte Count (DLC) in Typhoid Fever
Contrary to traditional belief, leukopenia is present in only about 25% of typhoid fever cases, while most patients show normal white blood cell counts, and some may even demonstrate leukocytosis, especially in complicated cases. 1
Typical Hematological Findings in Typhoid Fever
Total Leukocyte Count (TLC)
- Leukopenia (WBC <4,000/mm³) occurs in only 20-25% of cases 1, 2
- Normal WBC count is most common presentation
- Elevated WBC count (>8,000/mm³) may indicate complications with up to 70% of patients with leukocytosis developing complications 1
- A single WBC measurement is insufficient; serial monitoring is more valuable
Differential Leukocyte Count (DLC)
- Neutropenia occurs in approximately 25% of cases 1
- Relative lymphocytosis is traditionally described but absolute lymphocytosis is rare
- True lymphopenia is actually common, occurring in about 75% of patients 1
- Eosinophil count is typically normal or decreased (absence of eosinophilia helps differentiate typhoid from other tropical diseases) 3
Clinical Significance
Diagnostic Value
- TLC and DLC have limited diagnostic value for typhoid fever due to variable patterns
- Normal or decreased leukocyte count with abnormal liver function tests is a common pattern in typhoid fever 4
- Full blood count may be normal or deranged in almost any pattern 5
Prognostic Value
- WBC count >8,000/mm³ correlates with increased risk of complications (70%) 1
- Complications such as gastrointestinal bleeding, intestinal perforation, and typhoid encephalopathy occur in 10-15% of patients 5
- Thrombocytopenia is the most common hematological complication, occurring in approximately 13% of cases 6
Mechanism of Hematological Changes
- Hemophagocytosis in bone marrow contributes to neutropenia, anemia, and thrombocytopenia 2
- Increased histiocytes phagocytizing neutrophils, RBCs, and platelets are seen in bone marrow of neutropenic/leukopenic patients 2
Monitoring Recommendations
- Serial monitoring of TLC and DLC is more valuable than a single measurement
- Rising WBC counts may indicate developing complications
- Declining platelet counts should prompt vigilance for bleeding complications
- Manual differential is preferred over automated counts for accurate assessment 3
Diagnostic Algorithm
- Obtain baseline CBC with differential at initial presentation
- Monitor TLC and DLC serially during treatment
- Interpret in context of clinical presentation:
- Normal/low WBC with fever: consistent with uncomplicated typhoid
- Rising WBC or WBC >8,000/mm³: evaluate for complications
- Falling platelet count: monitor for bleeding complications
- Remember that blood culture remains the gold standard for diagnosis (40-80% sensitivity) 5
- Bone marrow cultures have higher sensitivity than blood cultures for diagnosis 5
Common Pitfalls
- Relying solely on leukopenia for diagnosis (present in only 25% of cases)
- Expecting absolute lymphocytosis (rarely present)
- Using a single CBC measurement rather than monitoring trends
- Attributing normal WBC to absence of infection
- Overlooking the significance of elevated WBC as a marker for complications
Remember that while TLC and DLC provide valuable information, they should be interpreted alongside clinical features and other laboratory tests, with blood culture remaining the definitive diagnostic test for typhoid fever.