BACKGROUND Malaria is considered as the main differential diagnosis of acute febrile illness in the tropics, and alteration of various hematological parameters has been observed in patients with malaria.    AIM To ascertain if certain hematological parameters increase the probability of malaria in patients with acute febrile illnesses.   
 SETTINGS AND DESIGN Hospital based, prospective cohort study.   
 METHODS AND MATERIAL All consecutive in patients with fever of less than seven days in duration were included in the study. Patients where localizing cause for fever could be determined were excluded. Hematological parameters (Hemoglobin, Red cell distribution width (RDW), Leukocyte count, and platelet counts) were determined by using automated counter, and peripheral smear examination for malarial parasite was taken as gold standard for the diagnosis of malaria.    STATISTICAL ANALYSIS USED Diagnostic accuracy was measured by computing sensitivity, specificity, predictive values and likelihood ratios. The precision of these estimates was evaluated using 95% confidence intervals.   
 RESULTS AND CONCLUSIONS A total of 184 patients were included in the study and 70 (38%) had a positive peripheral smear for malarial parasite. Thrombocytopenia alone (platelet countless than 150,000/mm3) was a predictor for malaria (Sn 60%, Sp 88%, LR+ 5.04) and in combination with anemia (Hb < 10 g/dl) it was next best parameter (Sn 69%, Sp 74%, LR+ 2.77). RDW and leukocyte count were not predictive. The conclusion of this study is that the presence of thrombocytopenia in a patient with acute febrile illness increases the probability of malarial infection.
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