Blood Culture, Routine
Culture, Blood, Routine
Isolate and identify potentially pathogenic organisms causing bacteremia; establish the diagnosis of endocarditis.
Additional Test Information:
Sequential blood cultures in nonendocarditis patients using a 20 mL sample resulted in an 80% positive yield after the first set, a 90% yield after the second set, and a 99% yield after the third set. Volume of blood cultured seems to be more important than the specific culture technique being employed by the laboratory. The isolation of coagulase-negative Staphylococcus poses a critical and difficult clinical dilemma. Although coagulase-negative Staphylococcus is the most commonly isolated organism from blood cultures, only a few (6.3%) of the isolates represent “true” clinically significant bacteremia. Conversely, coagulase-negative Staphylococcus is well recognized as a cause of infections involving prosthetic devices, cardiac valves, CSF shunts, dialysis catheters, and indwelling vascular catheters. Ultimately, the physician is responsible for determining whether an organism is a contaminant or a pathogen. The decision is based on both laboratory and clinical data. Frequently this determination includes patient data (ie, patient history), physical examination, body temperatures, clinical course, and laboratory data (ie, culture results, white blood cell count, and differential). The number of positive cultures as defined by a venipuncture is the most relevant criterion to use in determining whether an isolate is a contaminant. Clinical experience and judgment may play a significant role in resolving this clinical dilemma.
In patients who have received antimicrobial drugs, four to six blood cultures may be necessary. Any organism isolated from the blood is usually tested for susceptibility. It is not recommended to culture blood while
Adult: 16 to 20 mL total; 8 to 10 mL per aerobic and anaerobic bottle. Pediatric: up to 4 mL in one pediatric bottle; as age increases so should the volume of blood collected. Do not add more than 10 mL of blood to either the aerobic or anaerobic bottles, or more than 4 mL of blood to a pediatric bottle. The aerobic bottle has no minimum volume requirement.
One aerobic and one anaerobic blood culture bottle for adults or one pediatric bottle. Do not vent.
The major difficulty in interpretation of blood cultures is potential contamination by skin flora. This difficulty can be markedly reduced by careful attention to the details of skin preparation and antisepsis prior to collection of the specimen.
Skin preparation: First cleanse the venipuncture site with isopropanol. Then use an antiseptic swabstick to disinfect the site, using progressively larger concentric circles. This prepping agent should remain in contact with the skin for 30 seconds and be allowed to dry to ensure adequate disinfection. The venipuncture site must not be palpated after preparation. Blood is then safely drawn.
Use adult or pediatric blood culture collection kits provided by LabCorp. See the Procedural Chart for Blood Culture Collection provided in each collection kit for detailed information regarding bottle preparation, venipuncture, and bottle inoculation. Blood cultures should be drawn prior to initiation of antimicrobial therapy. The time of collection must be indicated. Strict aseptic technique is essential. If more than one culture is ordered, the specimens should be drawn separately at no less than 30 minutes apart to rule out the possibility of transient bacteremia due to self-manipulation by the patient of mucous membranes in the mouth caused by brushing teeth, etc, or by local irritations caused by scratching of the skin.
Suspected sepsis, meningitis, osteomyelitis, arthritis, listeriosis, or acute untreated bacterial pneumonia: Obtain two blood cultures from two different sites, such as the left and right arms.
Fever of unknown origin such as that caused by an occult abscess: Obtain two blood cultures initially. If those are negative, obtain two more 24 to 36 hours later. The yield beyond three or four cultures is virtually nil in this condition.
Suspected early typhoid fever and brucellosis: Obtain four blood cultures during 24 to 36 hours due to low-grade bacteremia involved in these rarely seen diseases.
Endocarditis (acute infective endocarditis): Obtain three blood cultures from three separate venipuncture sites during the first one to two hours and begin therapy.
Subacute infective endocarditis: Obtain three blood cultures within the first 24 hours, ideally within no less than hourly intervals. If all are negative at 24 hours, obtain two more. The yield beyond five blood cultures in subacute and endocarditis is virtually nil.
Maintain specimen at room temperature. Do not refrigerate.
Unlabeled specimen or name discrepancy between specimen and request label; bottles received broken; blood culture bottles received after a prolonged delay (usually more than 72 hours); blood not received in blood culture bottles; expired blood culture bottle