Blood culture

Blood culture is microbiological culture of blood. It is employed to detect infections that are spreading through the bloodstream (bacteremia, septicemia).
Indications: · Core temperature out of normal range · Focal signs of infection · Tachycardia, hyper or hypotension or raised respiratory rate · Chills or rigors · Raised or very low WCC · New or worsening confusion
N.B. signs of sepsis may be minimal or absent in the very young and the elderly.
Purpose To establish diagnosis in suspected septicaemia, endocarditis, bacterial meningitis, pericarditis, septic arthritis, osteomyelitis, pyelonephritis or enteric fever.
To identify the causative organisms in severe pneumonia, postpartum fever, pelvic inflammatory disease, cannulae sepsis, neonatal epiglottitis and sepsis. Investigations of patients with pyrexia of unknown origin (PUO). However, negative growths do not exclude infection.
The test 2-3 specimens of 20 ml of blood (2-4ml for infants, depending on weight) collected from separate sites within an hour (unless ?sepsis, fungal infections, endocarditis or endovascular (catheter related), when they should be at least an hour apart), cultured in enriched broth for aerobes, anaerobes and yeasts. Ideally, the sample is collected at the pyrexial peak and prior to antibiotic therapy. Where antibiotics have been commenced the samples should be taken immediately before the next dose. Blood cultures should not be routine.
Incubation is for 5-7 days (although most pathogens will grow within 1-2 days) and often extended for 14-21 days for suspected bacterial endocarditis, Brucella or yeasts. Growth is detected by the presence of turbidity, haemolysis, Gram stain or more commonly production of carbon dioxide or change in pH (detected by an automated monitoring system).
Risks The usual risks of venepuncture and the occurrence of false positive results (3+%) leading to inappropriate treatment (Madeo et al, 2003).
Procedure 1. Assemble the equipment, check bottles for damage, check expiry date on bottles and wash hands as per policy 2. Check the patients identity 3. Explain, check for needle phobia and gain consent 4. Clean visibly soiled skin with soap and water 5. Check patient is comfortable 6. Clean the bottle tops using a separate alcohol/ chlorhexidine wipes, as below, and discard these wipes 7. Apply tourniquet (disposable in the Southern Area) and select vein. 8. Cleanse for 30+ seconds with 2% chlorhexidine gluconate in 70% isopropyl alcohol (e.g. Clinelle) and allow to dry passively (Mimoz et al,1999, Pratt et al 2007). If central line is being used disinfect access port with 2% chlorhexidine gluconate in 70% isopropyl alcohol 9. Glove with clean gloves. Do not palpate vein following cleaning. Sterile gloves are not required. 10. Collect blood culture sample first (prior to other bloods) using closed system (e.g. Bio-Merieux holder for BacT/ALERT blood culture and safety blood collection set + luer adapter safety butterfly). Collect the aerobic sample first (10mls) and then 10mls into the anaerobic . Babies should have a single yellow ‘pedibact’ bottle used (aerobic) and an anaerobic sample. Ensure the bottle is positioned below the puncture site to avoid reflux of the broth into the patient Do not take blood from existing peripheral cannulae or from immediately above cannulae sites. Do not use the femoral vein.
11. Rotate the blood cultures bottles to mix –do not shake 12. Do not change needles between vein and bottles (this risks contamination) 13. Apply dressing to site and apply white nail pressure for 2+ minutes 14. Dispose of sharps carefully as per local policy 15. Label sample noting time and site i.e. peripheral, central line etc. in both the bottle and form, record and transport to laboratory ASAP. Do not obscure the bar code on the bottle 16. Record the date, time and site of specimen collected in the patient’s notes. 17. Ensure any spillages are cleaned up as per local policy 18. Wash hands again
Avoid using needles and syringes for this procedure as they risk needle stick injuries, over or under fill of bottles and accidental contamination.
Other steps: · Training for all participating staff · Competency assessment
References:
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
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.