| Blood culture | |
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| Intervention | |
Blood culture |
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| ICD-9: | 90.52 |
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.
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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 (3+%) leading to inappropriate treatment (Madeo et al., 2003).
A minimum of 10 ml of blood is taken through vein puncture and injected into two or more "blood bottles" with specific media for aerobic and anaerobic organisms.
The blood is collected using clean technique. This requires that both the tops of the culture bottles and the venipuncture site of the patient are cleaned prior to collection with alcohol swabs containing 2% chlorhexidine and 70% isopropyl alcohol.
To maximise the diagnostic yield of blood cultures multiple sets of cultures (each set consisting of aerobic & anaerobic vials filled with 3-10 mL) may be ordered by medical staff. A common protocol used in US hospitals includes the following:
Ordering multiple sets of cultures increases the probability of discovering a pathogenic organism in the blood and reduces the probability of having a positive culture due to skin contaminants.
After inoculating the culture vials, they are sent to the clinical pathology microbiology department. Here the bottles are entered into a blood culture machine, which incubate the specimens at body temperature. The blood culture instrument reports positive blood cultures (cultures with bacteria present, thus indicating the patient is "bacteremic"). Most cultures are monitored for 5 days after which negative vials are removed.
If a vial is positive, a microbiologist will perform a Gram Stain on the blood for a rapid, general ID of the bacteria, which they will report to the attending physician of the bacteremic patient. The blood is also subcultured or "subbed" onto agar plates to isolate the pathogenic organism for culture and suceptibility testing, which takes up to 3 days. This culture & sensitivity (C&S) process identifies the species of bacteria. Antibiotic sensitivities are then assessed on the bacterial isolate to inform clinicians on appropriate antibiotics for treatment.
[1] Some guidelines for infective endocarditis recommend taking up to 6 sets of blood for culture (around 60 ml).
Department of Health (2007) Saving lives: Reducing infection, delivering clean and safe care London: DoH
Donnino, M., Goyal, N., Terlecki, T., Donnino, K., Miller, J., Otero, R. and Howell, M. (2007) Inadequate blood volume collected for culture: A survey of health care professionals Mayo Clinic Proceedings 82(9) 1069-1072
Madeo, M. and Barlow, G. (2008) Reducing blood-culture contamination rates by the use of a 2% chlorhexadine solution applicator in acute admission units Journal of Hospital Infection 69, 207-309
Madeo, M, Davies, D., Owen, L., Wadsworth, P., Johnson, G. and Martin, C. (2003) Reduction in the contamination rate of blood cultures collected by medical staff in the accident and emergency department Clinical effectiveness in Nursing 7, 30-32.
Madeo, M., Jackson, T. and Williams, C. (2009) Simple measures to reduce the rate of contamination of blood cultures in accident and emergency Emergency Medicine Journal 22, 810-811.
Mimoz, O., Karim, A., Mercat, A. Cosseron, M., Falissard, B., Parker, F., Richard, C., Samii, K. and Nordmann, P. (1999) Chlorhexidine compared with providone-iodine a ski preparation before blood culture Annals of Internal Medicine131(11), 834-837
Shore, A and Sandoe, J (2008) Blood Cultures Student BMJ 16, 324-325
Pratt et al. (2007) epic 2: National Evidence Guidelines for preventing healthcare associated infections in NHS hospitals in England Journal of Hospital Infection 65 (1) S14
Weinstein, M.P., Lee, A., Mirrett, S. and Barth Reller, L. (2007) Infections in adults: How many blood cultures are needed? Journal of Clinical Microbiology 45, 3546-3548.