A recent study shows that refrigeration of urine at 5 degrees C for 24 hours does not significantly decrease the colony forming unit (CFU) counts in dogs with signs of urinary tract infection (UTI). Dr Mark Acierno and colleagues at LSU found that bacterial growth was 35.7% in immediately processed samples and 33.7% in refrigerated samples, but that refrigeration in tryptic soy broth (TSB) resulted in bacterial growth in only 31.7% of the samples. Thus, the sensitivity of culture of refrigerated samples compared to non-refrigerated samples was 95% but only 89% in refrigerated samples in TSB. For best results, we recommend that urine samples be submitted as undiluted urine or on a culture swab, and not in broth.
Urine sediment may deteriorate with time irrespective of refrigeration as crystal may form or dissolve depending on the pH of the urine. Refrigeration will tend to preserve cells and possibly slow bacteria overgrowth in free catch samples. Erythrocytes may lyse due to osmolal stress especially in dilute samples.
If a cytologic exam is desired, please make an air-dried sediment slide, since this will preserve cell integrity and prohibit bacterial overgrowth.
Abstract: JAVMA, Acierno, MJ et al, 7/15/2018:Vol 253, No. 2, pgs 177-180.