Introduction: Diagnosis of infection based on blood culture alone is not a suitable method, but it is important to understand the clinical diagnosis for interpreting blood cultures. The goal of this study was to determine blood culture contamination and the type of microorganisms in false and real positive cases in patients admitted at Avicenna Hospital. Methods: This cross sectional study was done on all patients in the emergency and internal medicine departments from April, 2008 to October, 2008 and blood for blood culture was obtained (in response to clinicians order) at least 2 times from two separate sites. Results: From 244 cases of blood culture, 62 cases (25%) were false positive, 31 cases (12%) were true positive and other cases are negative. Pseudomonas was the commonest organism in false positive cases followed by staphylococcus. Conclusion: There is a need for a close relationship between microbiology laboratory and clinical departments in order to avoid additional costs and also, cross- training for blood cultures.

Keywords: Culture Techniques; Blood, Microbiology; False positive Reaction

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