Blood culture & sensitivity

Synonym

Tubes

Obtain appropriate blood culture bottles for aerobic, anaerobic and where indicated Fungal or Acid Fast Bacillus (AFB) culture bottles [Aerobic blood cultures may be adequate for fungal culture; consult your laboratory]
Adults: 10-20 mL of blood (usually venous)
Children: 1-5 mL of blood (usually venous)

Additional information on specimen collection:

Sterilize the skin utilizing betadine (must dry before drawing specimen) or chlorhexidine (superior to betadine)
Wear gloves while handling specimen
Send to the laboratory immediately after collection
Do not draw from an IV catheter
Whenever possible, collect specimen before administering antimicrobial agents (however, do not delay antimicrobials for collection in critically ill patients)
Multiple samples may be indicated; collected at different times from different veins. Depending upon the underlying condition; the number of blood cultures indicated differs substantially.

Info

Blood cultures are used to diagnose or potentially exclude bacteria, fungi or other organisms circulating in the blood stream
Normally the blood does not contain any pathogens such as bacteria, fungi, viruses, and parasites.
A blood culture test detects and identifies microorganisms in the blood
The sensitivity component is performed when an organism is detected, to determine which antimicrobial agent(s) the organism is killed by (sensitive to) and not killed by (resistant to)
The identification of the organism can guide empiric antimicrobial therapy based upon typical antimicrobial sensitivities; Whereas sensitivities provide specific data on the isolated organism that can guide antimicrobial therapy

Clinical

Indications for blood culture/sensitivity test include:

Confirmation, diagnosis or potential exclusion of bacteremia or septicemia
Identifying the antibiotics that the infecting organism may be susceptible to
Evaluation of febrile patients without a clear cause
Evaluation of patients with febrile or sepsis syndromes who may be at high risk of bacteremia:

Late confirmation of diagnosis for epidemiological purposes (e.g. for predicting the appropriate constituents for a polyvalent influenza vaccine), where viral and fungal cultures take longer time to grow
Shock of suspected infectious etiology

Additional information:

Most organisms can be isolated in about 72 hours
Bacterial cultures are usually incubated for 5-7 days before being declared negative
Positive cultures do not necessarily indicate pathologic septicemia as many patients may have a mild transient bacteremia depending upon the clinical history and risk factors
If the isolated organism from the culture shows resistance to a particular antibiotic used in the sensitivity analysis; that antibiotic is typically not an effective treatment for the condition
False positive results can be caused by inadequate skin sterilization
False negative results can occur due to previous or current antimicrobial therapy
Related laboratory test includes a complete blood count

Nl Result

Reference value:

Negative or no growth of pathogens

High Result

Positive findings are commonly seen in:

Subacute Bacterial Endocarditis (SBE) [Most common in drug users, body piercing, dental work, prosthetic joints or heart valve abnormalities]

References

Dautle MP et al. In Vitro Antibiotic Sensivity and Resistance of 100 Clinical Bacterial Isolates Purified from Microbial Biofilms Associated with Silicone Gastrostomy Tubes Removed from Pediatric Patients. The Journal of Applied Research. 2004;4(1):50-59
Janjindamai W et al. Time to positivity of blood culture in newborn infants. Southeast Asian j Trop Med Public Health. 2006 Jan;37(1):171-6.
Kumar Y et al. Time to positivity of neonatal blood cultures. Arch Dis Child Fetal Neonatal Ed. 2001 Nov;85(3):F182-6.
Lamy B et al. What is the relevance of obtaining multiple blood samples for culture? A comprehensive model to optimize the strategy for diagnosing bacteremia. Clin Infect Dis. 2002 Oct 1;35(7):842-50. Epub 2002 Sep 10
Mimoz, O, et al. Chlorhexidine Compared with Povidone-Iodine as Skin Preparation before Blood Culture. Annals of Internal Medicine. 1999, Dec 7;131(11):834-837.