Effects of storage time and temperature on quantitative culture of canine urine

Results of quantitative culture of 25 canine urine samples stored at different temperatures for varying periods (2, 4, 6, 12, and 24 hours) following collection were compared. Samples stored at room temperature (21 to 25 C) were unreliable for diagnostic quantitative culture after 24 hours. False-positive results were obtained in 13 (50%) of the samples, and false-negative results were obtained in 1 (4%) sample. Likewise, samples sent via the US mail were unreliable for diagnostic quantitative culture since false-positive results were obtained in 9 (35%) of the samples. Samples stored at refrigeration temperature (3 to 8 C) provided more satisfactory data. Culture of urine samples refrigerated for 2 hours resulted in quantitative results that were similar and interpretations that were identical to those obtained for samples cultured without having been refrigerated. Refrigeration for periods up to 6 hours resulted in qualitative counts that differed from those obtained after initial culture of the nonrefrigerated samples, but interpretations of results were identical. After 24 hours of refrigeration there were no false-positive results; however, false-negative results were observed in 1 (4%) of the samples. These observations indicated that optimal results of quantitative culture of urine can be consistently obtained only if samples are immediately processed following collection. If immediate culture is not possible, the specimens may be stored for at least 6 hours at refrigeration temperature without compromising the validity of results.