Evaluation of preservative fluid for urine collected for culture

Abstract

Immediate culture or refrigeration of urine is recommended, but not always practical. Therefore, we evaluated the Becton-Dickinson Urine Culture Kit containing a boric acid-glycerol-sodium formate preservative in a study of 1,000 clinical urine specimens. Each specimen was cultured a total of four times by the surface streak technique with a 0.001-ml calibrated loop. After an initial reference culture (culture 1), a portion of urine was poured into a clean nonsterile paper cup, aspirated into a urine transport tube, and recultured immediately (culture 2). The original specimen cup was refrigerated for 18 to 24 hr (culture 3), and the urine transport tube was held at room temperature for 18 to 24 hr (culture 4) before repeat cultures. Eighty-eight of the initial reference cultures were positive (pure growth of >105 bacteria per ml). Eighty-two (93.2%) of the 88 specimens positive on the reference culture were also positive after refrigeration or holding at room temperature in the transport tube for 24 hr. There was one false-positive culture from refrigerated urine but none from the transport tube. Mixing of urine in a nonsterile container did not introduce detectable contamination. We conclude that the Becton-Dickinson Urine Culture Kit maintains a stable bacterial population in urine for up to 24 hr as reliably as refrigeration. Urine for culture may be collected in a nonsterile container if it is immediately aspirated into the transport tube so that contaminants are not allowed to multiply.