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).
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)..
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.