Comparison of blood cultures obtained simultaneously by venepuncture and from vascular lines

This study was designed to compare blood cultures drawn simultaneously from a pulmonary artery line or arterial line (line) and a peripheral site by venepuncture (VP). Two or three cultures were obtained by VP and from a line during each febrile episode in 79 patients. Line blood cultures were falsely negative in 1.3% of cultures and VP blood cultures were falsely negative in 2.0%. Three point eight per cent of blood cultures drawn from lines were falsely positive (contaminated), and 1.7% of VP cultures were falsely positive. No significant correlation was found between falsely positive line cultures and a positive three-way tap culture, line in use for 4 days or more, insertion of line during an emergency. We recommend that in the critically ill patient an arterial or pulmonary artery line may be used for obtaining reliable cultures.