Introduction Sepsis is one of the major causes of death in intensive care unit (ICU). One of the most important treatment for sepsis is antibiotic treatment. At the beginning antibiotics is chosen empirically after that is changed according to culture results or response to initial treatment. Nevertheless, only small number of culture positivity can be detected. The factors associated culture positivity are of interest in the critically ill patients. Therefore, we aim in our study to explore the factors associated with blood culture positivity especially blood glucose levels at the time blood culture sampling. Methods We perform this prospective observational study at the Intensive Care Unit of Dr. Suat Seren Chest Disease and Chest Surgery Training and Research Hospital between August 1, 2016 and January 1, 2017, in İzmir, Turkey. Two separate samples from opposite sides of each patient were obtained, and blood glucose was measured simultaneously with bed-side blood glucose measurement device by using the blood drawn for blood culture for each vial. The average of the two measurements was considered as the simultaneous blood glucose level of the patient. Results 174 patients were enrolled into the study, blood culture positivity was detected in 53 (30%) patients. In univariate analyzes, blood glucose levels, presence of central venous catheter, antibiotic treatment, vasoactive drug infusion and diabetes mellitus (DM) were associated with culture positivity. In multivariate analyze only DM was associated culture positivity (OR 5.63 [95% CI 1.99-15.91] p=0,001). Conclusion DM increase possibility of blood culture positivity. It stems from uncontrolled DM. Further studies are needed to evaluate this condition stems from uncontrolled DM or both uncontrolled and well-controlled DM.