A blood culture is a test on a sample of blood to check for bacteria in the bloodstream; it may be done if a doctor suspects a blood infection. A blood culture may be helpful in determining the specific bacteria causing an infection and selecting 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 indicate there may be bacteria in the blood.
It usually takes between 1 and 3 days to get the results of a blood culture; however, it can take as long as 7 to 10 days.
WebMD Medical Reference from Healthwise