Blood cultures are often prescribed in the hospital setting, even if their yield is weak. It's important to try to predict which patient will really benefit from them. There are some parameters that increase the chances of positivity of a blood culture, such as septic choc, chills or suspicion of Staphylococcus aureus bacteremia. Fever is not indicative. There are some clinical scores that permit to determinate the probability of a blood culture's positivity ; they haven't a high specificity, thus allowing mainly to avoid the taking of blood cultures whose risk of being negative is high. A new subject of interest in the field of infectious disease is the prediction of a resistant-organism bacteremia. This article aims to summarize the main predictions that we can draw when it comes to evaluate the utility of collecting a blood culture.