A blood culture is performed to isolate and aid identification of the pathogens in bacteremia (bacterial invasion of the bloodstream) and septicemia (systemic spread of such infection). It requires inoculating a culture medium with a blood sample and incubating it.
Gloves; tourniquet; small adhesive bandages; alcohol swabs; povidoneiodine swabs; 10- to 20-ml syringe for an adult, 6-ml syringe for a child; three or four sterile needles; two blood culture bottles, one vented (aerobic) and one unvented (anaerobic), with nutritionally enriched broths and sodium polyethanol sulfonate added, or bottles with resin or a lysis-centrifugation tube
Procedure and posttest care
Normally, blood cultures are negative for pathogens.
Positive blood cultures don't necessarily confirm pathologic septicemia. Mild, transient bacteremia may occur during the course of many infectious diseases or may complicate other disorders. Persistent, continuous, or recurrent bacteremia reliably confirms the presence of serious infection. To detect most causative agents, blood cultures are ideally drawn on 2 consecutive days.
Isolation of most organisms takes about 72 hours; negative cultures are held for 1 or more weeks before being reported negative.
Common blood pathogens include Streptococcus pneumoniae and other Streptococcus species, Haemophilus injluenzae, Staphylococcus aureus, Pseudomonas aeruginosa, Bacteroidaceae, Brucella, Enterobacteriaceae, coliform bacilli, and Candida albicans. Although 2% to 3% of cultured blood samples are contaminated by skin bacteria, such as Staphylococcus epidermidis, diphtheroids, and Propionibacterium, these organisms may be clinically significant when isolated from multiple cultures or trom immunocompromised patients.
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