What is the role of Total Leukocyte Count (TLC) and Differential Leukocyte Count (DLC) in diagnosing and managing leptospirosis?

Role of TLC and DLC in Leptospirosis

In leptospirosis, a polymorphonuclear leukocytosis (elevated TLC with neutrophil predominance) is a common finding and can help in diagnosis and prognosis, with WBC counts >14,000 cells/mm³ being a significant predictor of severe disease. 1, 2

Diagnostic Value of TLC and DLC

Initial Presentation

• Polymorphonuclear leukocytosis is a common but non-specific finding in leptospirosis 1
• Normal to elevated total leukocyte count is typically observed, with neutrophil predominance 1, 3
• A left shift (increased band neutrophils) may be present, indicating active infection 4

Prognostic Significance

• WBC count >14,000 cells/mm³ is associated with:
  • 5.12 times higher odds of severe disease (OR = 5.12,95% CI 2.75,9.51) 2
  • Likelihood ratio of 3.7 for bacterial infection 4
• Elevated leukocyte counts from day 4-5 of illness significantly correlate with severe disease (p=0.001) 3

Pattern of Changes in Blood Counts

TLC (Total Leukocyte Count)

• Initial phase: May be normal or slightly elevated
• Immune phase: Progressive increase, especially in severe cases
• Serial monitoring shows increasing TLC trend in severe disease 3

DLC (Differential Leukocyte Count)

• Neutrophil predominance is typical
• Band neutrophils >16% of total neutrophils or >1,500 cells/mm³ indicates a significant left shift 4
• Absence of eosinophilia helps differentiate from other tropical diseases 1

Associated Hematological Findings

Thrombocytopenia

• Significant predictor of disease severity:
  • Platelet count <100,000/μL increases odds of severe disease by 8.37 times 2
  • More pronounced in severe disease (p=0.002) 3
  • Present in 56% of leptospirosis cases 5

Anemia

• Progressive decline in hemoglobin from day 1 to day 7 3
• Hematocrit ≤30% associated with 3.49 times higher odds of severe disease 2

Clinical Application in Management

Diagnostic Algorithm

1. Obtain complete blood count with differential in suspected cases
2. Look for:
   • Polymorphonuclear leukocytosis
   • Thrombocytopenia
   • Progressive anemia
3. Correlate with clinical features:
   • Jaundice (increases odds of severe disease by 3.11 times) 2
   • Renal dysfunction (more common with thrombocytopenia - 71.42% vs 18.18%) 5
   • Respiratory manifestations (ARDS more common with thrombocytopenia - 86.6% vs 13.33%) 5

Monitoring Disease Progression

• Serial CBC monitoring is essential to detect:
  • Rising WBC counts (indicating worsening infection)
  • Declining platelet counts (risk of bleeding)
  • Falling hemoglobin (anemia)

Pitfalls and Caveats

• TLC and DLC changes are non-specific and must be interpreted alongside clinical features and serological tests
• Normal WBC count does not rule out leptospirosis
• Manual differential is preferred over automated counts to accurately assess band forms 4
• Confirmation of diagnosis requires serological testing (IgM ELISA, MAT) or culture 1
• Treatment decisions should not be delayed waiting for confirmatory tests if clinical suspicion is high 1

Summary of Key Points

1. Polymorphonuclear leukocytosis is common but not universal in leptospirosis
2. WBC >14,000 cells/mm³ is a significant predictor of severe disease
3. Thrombocytopenia and progressive anemia frequently accompany leukocyte changes
4. Serial monitoring of complete blood counts helps track disease progression
5. CBC findings should guide early treatment decisions while awaiting confirmatory tests