What are the typical complete blood count (CBC) findings in typhoid fever and how is it managed?

CBC Findings in Typhoid Fever and Management

In typhoid fever, the most common CBC findings include leukopenia with neutropenia and relative lymphocytosis, thrombocytopenia, and anemia, though these findings are not universal and normal white blood cell counts may be present in many cases.

Typical CBC Findings in Typhoid Fever

White Blood Cell (WBC) Abnormalities

• Leukopenia: Present in approximately 25% of patients 1, 2
• Normal WBC count: Found in majority of cases (approximately 75%) 1
• Neutropenia: Occurs in about 25% of patients 1
• Relative lymphocytosis: Common, though absolute lymphocytosis is rare 2
• Absolute lymphopenia: Present in up to 75% of cases 1
• Increased immature bands: May be observed even when total WBC count is normal 3

Platelet Abnormalities

• Thrombocytopenia: Common finding, can sometimes be the presenting sign 4, 5
• Platelet counts: May decrease significantly in infected individuals compared to healthy controls 5

Red Blood Cell Abnormalities

• Anemia: Frequently observed 5, 6
• Decreased packed cell volume (PCV): Significant reduction compared to non-infected individuals 5

Pathophysiological Mechanisms

The hematological changes in typhoid fever are attributed to several mechanisms:

• Bone marrow suppression: Direct effect of Salmonella typhi infection 5
• Hemophagocytosis: Increased histiocytic activity with phagocytosis of blood cells (neutrophils, red blood cells, and platelets) 6
• Immune-mediated destruction: May contribute to cytopenias

Diagnostic Value of CBC Findings

• A normal leukocyte count (OR 10.8) or count <10.0 × 10³/mm³ (OR 30.2) is strongly associated with typhoid fever 2
• Leukopenia due to absolute neutropenia with relative lymphocytosis, when present, is highly suggestive of typhoid fever 2
• A leukocyte count >10.0 × 10³/mm³ provides strong presumptive evidence against typhoid fever diagnosis (OR 0.03) 2

Management of Typhoid Fever

Diagnostic Approach

1. Blood cultures: Gold standard for diagnosis with highest yield within the first week of symptoms 3, 7
2. Complete blood count: Essential for evaluation and monitoring 3
3. Stool and urine cultures: Become positive after the first week (sensitivity: stool 35-65%, urine 0-58%) 3, 7
4. Bone marrow cultures: Higher sensitivity than blood cultures in difficult cases 3, 7

Treatment Recommendations

1. First-line empiric therapy:

   • For patients from Asia: Intravenous ceftriaxone (due to high rates of fluoroquinolone resistance) 3
   • For patients from Africa: Ciprofloxacin may remain an alternative 3

2. Duration of treatment: 14 days to reduce risk of relapse 3

3. Oral step-down therapy options:

   • Azithromycin: For confirmed fluoroquinolone-resistant cases 3
   • Ciprofloxacin: For confirmed sensitive isolates (provides most effective treatment with fever clearance <4 days and cure rates >96%) 3

4. Monitoring during treatment:

   • Regular CBC to monitor resolution of hematological abnormalities
   • Platelet counts typically normalize within the first week of appropriate antibiotic therapy 4

Clinical Pearls and Pitfalls

• Pitfall: Relying solely on CBC findings for diagnosis - while suggestive, they are not specific enough for definitive diagnosis
• Pitfall: Using the Widal test for diagnosis - lacks sensitivity and specificity 3, 7
• Pearl: Consider typhoid in any returning traveler from endemic areas (particularly South/Southeast Asia) with fever and compatible CBC findings 3
• Pearl: Complications such as gastrointestinal bleeding, intestinal perforation, and encephalopathy occur in 10-15% of patients, especially if illness duration exceeds 2 weeks 3

Remember that while hematological parameters can provide valuable diagnostic clues, blood culture remains the gold standard for diagnosis of typhoid fever.