[Contamination of blood cultures drawn from central vein catheter and peripheral venipuncture. Prospective study of 75 pairs].

OBJECTIVE

To determine the frequency of contamination, the sensitivity, specificity, and predictive values of cultures done with blood drawn through a central venous catheter or peripheral venipuncture.

DESIGN

Prospective cohort study of critical ill medical surgical intensive care patients in whom samples for paired culture were drawn through a central venous catheter or peripheral venipuncture during a period of 8 months (from August 1st 2001 to Mars 31st 2002).

RESULTS

During the study period, 75-paired cultures were studied. Fifteen peripheral blood cultures (20%) and 27 central blood cultures (36%) were positive and 6 peripheral blood cultures (8%) and 15 central blood cultures (20%) were contaminated (P=0.034). The organism most commonly responsible for contamination was Coagulase Negative Staphylococcus (16% of central blood cultures and 6.7% of peripheral blood cultures). The frequency of contamination was of 42.9% for blood cultures drawn through a femoral central venous catheter, of 10% for jugular, and of 19% for subclavian central venous catheter (P=0.22). For catheter draws compared with peripheral venipuncture, sensitivity was 100 and 75%, specificity was 76.2 and 90.5%, positive predictive value was 44.4 and 60% and negative predictive value was 100 and 95%.

CONCLUSION

Cultures of blood drawn through a catheter are more sensible and less specific than those obtained from a peripheral venipuncture and the organism most commonly responsible for contamination of blood cultures is Coagulase Negative Staphylococcus.