What is the significance of leucocyte (white blood cell) count in a patient with typhoid fever?

Leucocyte Count in Typhoid Fever

In typhoid fever, leucopenia (low white blood cell count) is classically described but occurs in only about 25% of patients, while a normal or even elevated white cell count is more common and does not exclude the diagnosis. 1

Key Hematological Findings

White Blood Cell Patterns

• Leucopenia is present in only 24.6% of typhoid patients on admission, contrary to the traditional teaching that it is a common finding 1
• Normal or elevated white cell counts occur in the majority of patients (approximately 75%) and should not be used to rule out typhoid fever 1
• Neutropenia occurs in only 25% of patients, making it an unreliable diagnostic marker 1
• Relative lymphocytosis is classically described, but absolute lymphopenia is actually present in 75.8% of patients, which is the opposite of traditional teaching 1

Clinical Significance of Leucocyte Count

• Elevated white cell count (>8 x 10⁹/L) is associated with worse outcomes, with complications occurring in 70% of these patients compared to lower rates in those with normal or low counts 1
• The combination of fever with normal or decreased leukocyte count should raise suspicion for typhoid, particularly in travelers returning from endemic areas 2, 3
• Bradycardia with a normal leukocyte count is a particularly suggestive combination for typhoid fever diagnosis 2

Complete Hematological Profile

Additional Blood Count Abnormalities

• Thrombocytopenia (low platelet count) is a common finding in typhoid fever 4, 3
• Anemia is frequently observed in affected patients 4
• Eosinopenia (decreased eosinophils) occurs as part of the hematological response 4
• Subclinical disseminated intravascular coagulation may be present in some cases 4

Bone Marrow Changes

• Bone marrow examination shows myeloid maturation arrest, decreased erythroblasts and megakaryocytes, with increased phagocytic activity of histiocytes 4

Diagnostic Approach

Essential Laboratory Tests

• Full blood count should be obtained to look for lymphopenia and thrombocytopenia, which are more reliable than leucopenia 5
• Blood cultures remain the gold standard with 40-80% sensitivity, highest in the first week of illness 5
• Liver function tests typically show elevated SGOT/SGPT, which is one of the most common laboratory abnormalities 3
• Elevated inflammatory markers (ESR, CRP) are expected, though CRP elevation occurs despite normal white cell counts 2, 3

Critical Clinical Pitfall

Do not exclude typhoid fever based on a normal or elevated white blood cell count. The classic teaching of leucopenia as a hallmark of typhoid is outdated and applies to less than one-quarter of patients. Instead, focus on the clinical presentation (fever pattern, headache, abdominal symptoms), travel history, and obtain blood cultures for definitive diagnosis 2, 1, 3.