Microbiological evaluation of a commercial transport system for urine samples

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

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.

Comparison of Uriswab to alternative methods for urine culture collection and transport: confirmation of standard culture methodology for investigation of urinary tract infections

The ability to isolate and identify causative agents of urinary tract infections relies primarily on the quality of the urine sample that is submitted to the microbiology. The most important factors are the method of collection, the maintenance of viability of the potential pathogens during transport, and standardization of the culturing of the urine sample. This report is a composite of several investigations comparing collection and transport on urine culture paddles, with a preservative urine sponge (Uriswab), and a comparison of Uriswab with the BD preservative transport tube as methods of preservation of urinary pathogens. Primary studies showed that Uriswab maintained significantly more urinary pathogens than the urine culture paddle with fewer mixed or contaminated cultures. The two preservative transport systems were comparable for maintenance of viability of the pathogens, but there were fewer mixed cultures when samples were collected with Uriswab. This study confirms the importance of a standard volume of 1 μL of urine for culture.

A method for the rapid detection of urinary tract infections

OBJECTIVE

To determine the reliability of a rapid detection method compared with the reference standard streaked agar plate in diagnosing the presence of urinary tract infection (UTI).

METHODS

De-identified clean catch urine specimens from 980 office visit patients were processed during a 30-day period. Classic 1-μL and 10-μL streaked agar plates were used in parallel with the new CultureStat Rapid UTI Detection System (CSRUDS). Urine results were evaluated using the CSRUDS at 30 and 90 minutes after collection. A comparative analysis of the subsequent plate results versus the CSRUDS results was achieved for 973 of these samples.

RESULTS

Positive UTI conditions were accurately identified by both CSRUDS and agar streak plate methods. CSRUDS accurately identified UTI negative conditions with 99.3% reliability at 90 minutes. The negative predictive value of CSRUDS was 99.2% at 30 minutes.

CONCLUSION

Current agar plating for first-round UTI screening has substantial documented problems that can negatively affect an accurate and timely UTI diagnosis. A novel rapid detection system, the CSRUDS provides UTI negative/positive same-day results in ≤ 90 minutes from the start of test. Such rapidly available results will enable more accurate and timely clinical decisions to be made in the urology office, particularly regarding infection status before urologic instrumentation.

Limits of preservation of samples for urine strip tests and particle counting

BACKGROUND

Preservation of urine samples is important for centralised laboratory services with automated instruments.

METHODS

A multicentre evaluation was carried out to assess preservative tubes from BD Diagnostics-Preanalytical Systems and from Greiner Bio-One for test strip reading (documented at the level of remission values), for particle counting by flow cytometers (UF-100) and for visual microscopy. Failures were expressed as percentages of originally positive samples beyond a two-fold change (+100% or -50%) from the original values.

RESULTS

The preservative-containing BD Plus C&S plastic, BD Plus UAP and Greiner Stabilur tubes succeeded in preservation of test strip results for 6-24 h (exceptions were glucose and nitrite tests). Greiner boric acid tube showed false negative results in leukocyte, protein and ketone strip tests immediately after adding the preservative. Urine red blood cell counts (with Sysmex UF-100) were preserved for 5 h in BD Plus C&S plastic and Greiner Stabilur tubes (Greiner tubes having clearly larger preservative-related background). Bacteria or white blood cell counting succeeded in BD Plus C&S plastic tubes for 5 or 24 h, respectively, but up to 72 h in Greiner Stabilur tubes. In visual microscopy, the Greiner Stabilur tube was slightly better than the BD Plus C&S plastic tube.

CONCLUSIONS

Urine specimens can be transported at +20 degrees C on the day of collection if preserved properly. Longer delays need careful planning with current preservatives. Flow cytometry with UF-100 is sensitive to non-dissolved preservative remnants.