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 h (culture 3), and the urine transport tube was held at room temperature for 18 to 24 h (culture 4) before repeat cultures. Eighty-eight of the initial reference cultures were positive (pure growth of greater than 10(5) 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 h. 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 h 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.