Purpose
Ensure blood collected for cultures is free from contamination (from patient or personnel), precautions are taken for skin preparation as well as collection tube preparation.
Policy
This procedure is for the additional collection of Blood Cultures. Follow the Blood Collection by Venipuncture, Vascular Access Devices (VAD), and Patient Identification and Laboratory Specimen Labeling procedures for all other steps.
Indications
Routine blood cultures should be performed on any patient in whom there is a suspicion of bacteremia or candidemia.
Isolator blood cultures should be performed on any patient suspected of having one of the following:
- Subacute or chronic endocarditis with multiple negative BACTEC system cultures. It is appropriate to use the BACTEC system for the initial workup of endocarditis of any suspected etiology. Isolators should be used after multiple BACTEC cultures are obtained and fail to reveal an etiologic agent (including HACEK).
- Suspected deep fungal infection, such as histoplasmosis, blastomycosis, and coccidioidomycosis. Ordinarily, cultures of other sites, such as tissue biopsy, and in some cases serological tests, are more helpful than blood culture.
- Suspected mycobacteremia, particularly in HIV patients with CD4 counts <50.
- Suspected disseminated gonococcal infection.
- Suspected bartonellosis.
- Suspected candidemia or disseminated cryptococcosis in patients for whom routine cultures have not detected Candida species or Cryptococcus neoformans, respectively.
- Suspected Malassezia furfur infection, an agent of catheter-associated infection in patients receiving intravenous lipid.
The indication for use of isolators should be given to the microbiology resident, who must approve the test.
The following is not an indication for blood cultures of either type:
Surveillance for infection before the clinical suspicion of infection exists.
Timing
Blood cultures should be drawn prior to the institution of antibiotics whenever possible. If empiric treatment is an emergency, blood cultures should still be drawn as soon as possible after institution of antibiotics. There are no data to suggest that the timing of culture in relation to the appearance of fever or chills will maximize the yield.
GUIDELINES FOR BLOOD CULTURE COLLECTION
Volume of blood per set
There is a direct relationship between the volume of blood obtained and the yield of a blood culture set. Forty to 60 ml of blood should be obtained per episode (in other words, 2-3 sets with 20 ml per set, and 10 ml per bottle).
Number of sets of blood cultures
Single sets should not be used to evaluate any patient with suspected bacteremia or candidemia. The optimal yield is obtained with two or three sets of blood cultures. No more than three blood cultures should be obtained for any given 24 hour period.
Procedure
Prepare for Collection
Complete initial steps for venipuncture or VAD collection, including identify patient, identify site/lumen, put on gloves, assemble supplies, etc.
CAUTION: Always use gloves and observe Standard Precautions when collecting biologic specimens.
Additional Supplies
- Chlorhexidine gluconate scrub (ChloraPrep®) or
- Povidone-Iodine swabstix (required if patient less than 2 months of age)
- Culture bottles or tubes
Select Appropriate Culture Bottle/Tube
Site of blood culture
Blood should be obtained from peripheral venous or arterial sites. Obtaining blood cultures from central venous catheters, arterial lines and inguinal vessels increases the likelihood of obtaining a false positive blood culture.
The practice of drawing blood for culture from catheters or the groin should never be performed when a peripheral (i.e., non-catheterized) site is available.
Labeling
Labeling the site of each set of blood cultures, particularly regarding whether a set was drawn from a catheter, the groin, or not, is of utmost importance in helping to distinguish pathogens from contaminants in those cases in which no peripheral access can be found.
Preparation of the site for culture
- After the vessel site is selected, a 5 cm area of skin should be disinfected by swabbing concentrically with 70% alcohol, from the venipuncture site outward.
- The site should be cleansed once again, this time with 10% povidone-iodine or 2% tincture of iodine again in a circular motion.
- Allow the iodine to dry completely before performing venipuncture. This should take 1 – 2 minutes.
- While waiting for the site to dry, the plastic cap covering each blood culture bottle should be removed, and the rubber stopper should be decontaminated with 70% alcohol. (Iodine solutions will disintegrate the rubber and should not be used.)
- 20 ml of blood should be withdrawn from the puncture site.
- Do not change needles between venipuncture and inoculation of the bottles, or between bottles. The risk of needlestick is increased, while the chance of contamination is not significantly lessened.
- Remove the iodine solution from the skin with alcohol. This will minimize the possibility of hypersensitivity.
Ramaz Mitaishvili, MD
Glendale, CA
