How long do blood cultures take?

24-48 hours: When blood cultures are taken, they are put into a machine that looks for bacteria growing. Most hospitals have machines that constantly are looking for growth. As soon as they turn positive, the machine alerts a technician and the alert goes out to the doctor. Most physicians consider 24-48 hours a reasonable time frame.

Depends: It depends on the type of organism, how many organisms were present in the blood at the time blood was drawn and if you were administered antibiotics before sample collection. Blood culture can turn positive in less than 24 hours, but the lab may wait up to five days to call it negative .If there is no growth of bacteria.