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Blood Cultures from Central Venous Catheters -- Easy, But Are They Good?
The use of indwelling central venous catheters (CVC) to administer medication and obtain blood samples has contributed to minimizing the discomfort of prolonged illnesses such as cancer. However, blood culturing through these devices has been discouraged for fear of increasing specimen contamination, thereby causing unnecessary work-ups and longer hospital stays.
These authors retrospectively compared 551 pairs of blood cultures obtained at a single medical center from peripheral venipuncture (PV) and CVC in 185 patients with cancer. Paired specimens were collected within 4 hours of each other; 2 infectious diseases consultants provided blinded assessments of the clinical relevance of positive or negative culture results.
Concordantly negative cultures were found in 469 of the pairs (85%); 82 paired cultures were positive. Of these, 6% were CVC positive/PV positive; 3% were CVC negative/PV positive; and 6% were CVC positive/PV negative. All 32 CVC-positive/PV-positive pairs (100%), 5 of 18 CVC-negative/PV-positive pairs (28%), and 10 of 34 CVC-positive/PV-negative pairs (29%) were clinically determined to indicate true bacteremia. Additional antibiotics targeted to perceived pathogens were more likely to have been given to patients with PV-negative cultures (50%) than to patients with CVC-negative cultures (20%).
Comment: The negative predictive value of cultures from CVC is very high (99%), but the positive predictive value is far lower (63%) and is also lower than that from PV. Because blood cultures are often drawn at the time of a fever spike, and empiric therapy is also started at that time, negative CVC cultures might be used as a marker for stopping empiric therapy soon after the patient defervesces.
— S Baum
Published in Journal Watch Infectious Diseases January 1, 2000
Citation(s):
DesJardin JA et al. Clinical utility of blood cultures drawn from indwelling central venous catheters in hospitalized patients with cancer. Ann Intern Med 1999 Nov 2 131 641-647.
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