Blood cultures

Blood culture
Intervention
Blood culture
ICD-9	90.52
MedlinePlus	003744
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Blood culture is a microbiological culture of blood. It is employed to detect infections that are spreading through the bloodstream (such as bacteremia, septicemia amongst others). This is possible because the bloodstream is usually a sterile environment.

Blood cultures were pioneered in the early 20th century.

When a patient shows signs or symptoms of a systemic infection, results from a blood culture can verify that an infection is present, and they can identify the type (or types) of microorganism that is responsible for the infection. For example, blood tests can identify the causative organisms in severe pneumonia, puerperal fever, pelvic inflammatory disease, neonatal epiglottitis, sepsis, and fever of unknown origin (FUO). However, negative growths do not exclude infection.

The usual risks of venipuncture and the occurrence of false positive results approximately 3%+ of the time, can lead to inappropriate treatment.

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. A common medium used for anaerobes is thioglycollate broth.

The blood is collected using aseptic technique. This requires that both the tops of the culture bottles and the venipuncture site of the patient are cleaned prior to collection by swabbing with 70% isopropyl alcohol (povidone and left to dry before venipuncture).

To maximise the diagnostic yield of blood cultures, multiple sets of cultures (each set consisting of aerobic and anaerobic vials filled with 3–10 mL) may be ordered by medical staff. A common protocol used in US hospitals includes the following:

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