Can findings on peripheral blood smear differentiate leptospirosis from other infections? A preliminary comparative study.

Background: Blood smear changes have never been investigated as a potential tool to aid in the diagnosis of leptospirosis.

Methods: Blood smears prepared from patients with leptospirosis, dengue and sepsis within the first 5 days of illness were reported by haematologists blinded to the diagnosis.

Results: A total of 20, 28 and 22 patients with leptospirosis, dengue and sepsis, respectively, were analysed. Neutrophil leucocytosis, toxic changes in neutrophils, left shift, reactive lymphocytes, target cells and thrombocytopaenia were seen in 60%, 70%, 40%, 70%, 50% and 65% of the leptospirosis patients, respectively. The combination of reactive lymphocytes with toxic neutrophils or neutrophil leucocytosis was highly suggestive of leptospirosis.

Conclusions: Peripheral blood smear findings may be helpful in differentiating leptospirosis from other common acute febrile illnesses.