A blood culture is a test on a sample of blood to check for bacteria, a fungus, or sometimes viruses in the bloodstream. The test may be done if a doctor suspects a blood infection. A blood culture may help determine the specific organism causing an infection and select the appropriate antibiotic to treat it.

Usually a blood culture is needed only if a person is severely ill. Blood cultures are commonly done when a person has a high fever or shaking chills that mean there may be an infection of the blood.

It usually takes between 1 and 3 days to get the results of a blood culture. But a blood culture to look for a fungus or virus can take weeks.