Blood culture

Overview
Blood culture is microbiological culture of blood. It is employed to detect infections that are spreading through the bloodstream (bacteremia, septicemia).

Method
A minimum of 10 ml of blood is taken through venipuncture and injected into two or more "blood bottles" with specific media for aerobic and anaerobic organisms.

Care needs to be taken that the bottles are not contaminated with bacteria from staff members or other patients. To that end, the patient's skin is rubbed or sprayed with denaturated alcohol and betadine applied to the sampling site. Sterile gloves should be used to minimize contamination.

To maximise the diagnostic yield of blood cultures, multiple samples are sometimes taken from different veins. The larger the amount of blood taken, the more likely it is that the causative organism is found. Some guidelines for infective endocarditis recommend taking up to 6 sets of blood for culture (around 60 ml).

Uses
Any infection causing fever may prompt hospital physicians to request blood cultures. Identifying the agent may aid in choosing the correct antibiotic and addressing particular risk factors.

Blood culture is essential in the diagnosis of infective endocarditis. In this elusive disease, blood cultures may have to be repeatedly taken during febrile episodes, when bacteria are shed from the heart valves into the bloodstream (bacteremia)..

History
Blood cultures were pioneered in the early 20th century. Gustav Mahler, the composer, was diagnosed with infective endocarditis close to the end of his life, but as this was before the introduction of antibiotics, it contributed to his (early) death.