The effect of urine storage temperature and boric acid preservation on quantitative bacterial culture for diagnosing canine urinary tract infection

Abstract

Background Quantitative bacterial culture (QBC) is the gold standard for diagnosing canine urinary tract infection. Current guidelines recommend QBC within 24 h of urine collection and that unpreserved urine is refrigerated until culture. However, temperature-controlled transport is rarely feasible, indicating a need for alternative storage during transport of urine from primary veterinary practices to the microbiology laboratory. The objective was to investigate the effect of storage temperature and boric acid sponge-preservation on quantitative bacterial culture of canine urine. Results Significant bacteriuria was detected in 72 out of 179 samples (40%) collected from 141 dogs. Overall accuracy was 94–98% for both storage conditions and time points. Non-inferiority (15% margin) to reference quantitative bacterial culture was evident for sensitivity, specificity and predictive values for both storage methods and time points, except for the negative predictive value for 48 h boric acid preservation (NPV: 89, 95% CI [79;95]). There was no significant difference between the sensitivity and specificity for either of the time-points (p-value = 0.07–1). Conclusions Boric acid sponge-preservation using Uriswab™ is a useful alternative to refrigeration of urine samples during transport. Reliable quantitative bacterial culture results can be obtained from canine urine up to 48 h after collection if urine is refrigerated, and for at least 24 h if urine is stored using a boric acid-containing urine transport system.

The impact of urine storage methods on the results of quantitative bacterial culture in dog and cat

“…Most studies collected dog urine samples only and some studies mixed dog and cat data for calculation (Padilla et al 1981;Acierno et al 2018;Coffey et al 2020). Some studies included voided urine samples for QBC, which was discouraged since contamination was possible (Coffey et al 2020;Neumann et al 2020;Hedstrom et al 2021). Some of the studies used preservatives such as boric acid which was not often used in clinical practice (Rowlands et al 2011;Hedstrom et al 2021).…”

“…Some studies included voided urine samples for QBC, which was discouraged since contamination was possible (Coffey et al 2020;Neumann et al 2020;Hedstrom et al 2021). Some of the studies used preservatives such as boric acid which was not often used in clinical practice (Rowlands et al 2011;Hedstrom et al 2021).…”

Die Urinuntersuchung bei Hund und Katze, Teil 1: Physikalische und chemische Urinuntersuchung

“…Um ein verlässliches Ergebnis zu erhalten, sollten bei gekühlt gelagerten Urinproben bakteriologische Untersuchungen innerhalb von 24 h nach der Uringewinnung durchgeführt werden [3,19,28]. Der Anteil falsch-negativer Ergebnisse nach 24-stündiger gekühlter Lagerung liegt bei 2-5 % [28,35,36], der Anteil falsch-positiver Ergebnisse bei bis zu 6 % [36].…”

“…Zur chemischen Konservierung von Urin stehen verschiedene Stoffe oder käuflich erwerbliche Kits zur Verfügung [25,29,36]. Chemisch konservierte Urinproben sollten nicht zur chemischen Urinuntersuchung verwendet werden, da die zugegebenen Stoffe mit Testfeldern auf dem Teststreifen interferieren können [38].…”

“…Die Konservierung mittels Borsäure eignet sich für Urinproben, welche einer bakteriologischen Untersuchung unterzogen werden sollen [2,36,37,39]. Borsäure wird in kommerziell erhältlichen Kits in der Regel mit Natriumformiat kombiniert, um ein bakteriostatisches Medium zu schaffen [2,29,36].…”