Quantitative bacterial culture (QBC) is the gold standard for diagnosing urinary tract infection (UTI). Current guidelines recommend that QBC is performed within 24 hours of collection and that urine, if unpreserved, is stored and transported at refrigeration temperatures. However, temperature-controlled transport is expensive and may not always be feasible in veterinary practice, indicating a need for alternative storage methods.

The aim of this study was to investigate the effect of storage temperature and boric acid preservation on QBC of canine urine.

The hypothesis was that i) urine stored non-preserved by refrigeration (COOL) or preserved in commercially available urine preservation swabs containing boric acid (Copan UriSwab^TM) at room temperature (BA-ROOM) for 24 and 48 hours, respectively, would be non-inferior to the reference QBC and that ii) there would be no significant difference in sensitivity and specificity of the two storage methods.

Canine urine samples received at the veterinary microbiology laboratory at UCPH between February 2015 and March 2016 were prospectively included in the study. After initial reference QBC, urine samples were split into three aliquots. Two aliquots were stored at room temperature in Copan UriSwab^TM, and one aliquot was stored refrigerated in an unpreserved microfuge tube, for 24 h and 48 h, respectively. Significant bacteriuria was determined with regard to urine collection method according to current recommendations.

Non-inferiority was concluded if the lower limit of the one-sided 95% confidence interval was above 85% (Δ=0.15). McNemar χ² test was performed to compare sensitivity and specificity for the two storage methods.

A total of 179 samples from 141 dogs were included. Significant bacteriuria was found in 42% of the samples according to reference QBC. With an overall accuracy of 94–97%, all storage conditions were non-inferior to reference QBC, except for BA-ROOM at 48 h which had an inferior sensitivity. However, there was no significant difference between the sensitivity of the two methods at the two time points (p=0.06–1.00).

The results show that boric acid preservation at room temperature is a valid alternative to refrigeration and that reliable QBC can be obtained after storage of canine urine for 24 h by both methods.

Disclosures

Disclosures to report
Copan UriSwab(^TM) kit kindly donated by Copan Italia