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The impact of Boric Acid tubes on quantitative urinary bacterial cultures in hospitalized patients.

Author(s): Ben-David D, Cohen Y, Zohar I, Maor Y, Schwartz O

Publication: Eur J Clin Microbiol Infect Dis, 2024, Vol. , Page

PubMed ID: 38916642 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   This study retrospectively compared bacterial growth positivity rates unmatched in urine specimens from hospitalized patients that were collected and stored in preservative-free containers and those collected and stored in boric acid tubes. The potential effects of patient sex and age, method of urine collection (indwelling catheter versus midstream), time of day of collection (day versus evening or night), and processing time (≤4 h versus 4-24 h or ≥24 h) on the culture positivity rate were also examined. A total of 9117 specimens collected prior to a change in collection container and 3543 specimens collected after the change were considered. Specimens were obtained as part of the care of hospitalized patients >18 years of age (no diagnosis specified). Prior to January 2022, urine was collected into pre¬servative-free containers and stored at room temperature before transport to the microbiological laboratory. From January 2022-Decem¬ber 2022, urine specimens were collected into boric acid BD Vacutainer tubes and transported via the pneumatic transport system. Urine was cultured on Blood Agar / CHROMagar Orientation plates and incubated overnight at 37° C. Specimens were classified as positive if there were ≥ 100,000 CFU/ml.

   Summary of Findings:

   Overall culture positivity rate was higher in urine specimens from women than men (31.0% versus 23.4%, p <0.001) and in specimens collected via indwelling urinary catheters versus midstream collection (31% versus 20.9%, p<0.001).  Additionally, the median patient age was higher from culture positive than negative specimens (83 versus 80 years, p<0.001). The percentage of positive cultures increased with increasing processing time (21.3% for <4 h, 28.4% for 4–24 h, and 32.9% for ≥24 h, p< 0.0001). A multivariate analysis identified an increased risk for culture positivity (Odds Ratio, OR) with increased patient age (OR=1.02, p<0.001), the patient being female versus male (OR =1.37, p<0.001), urine collection via indwelling catheter versus midstream (OR=1.41, p<0.001), collection during the evening (OR=1.37, p<0.001) or night (OR=1.25, p=0.03) versus the day, and a processing time >24 h versus <4 h (OR=1.69, p<0.001).  
   Specimens collected after the change to boric acid containing tubes had a lower culture positivity rate than those collected prior to the switch (in preservative-free tubes)(23.8% versus 28.9%, p<0.001); urine specimens collected in boric acid containing tubes  also had a higher percentage of specimens from male patients (52.1% vs. 48.5%, p < 0.001), a lower median patient age  (80 years vs. 81 years, p < 0.001), a lower median processing time (11 h versus 14 h, p<0.001), and a higher percentage of specimens processed with 4 h than those collected in preservative-free tubes(26% versus 21% and 16%, p<0.001). When the data was stratified by processing time, significantly fewer boric acid preserved specimens were culture positive than unpreserved specimens when processing occurred between 4-24 h post collection (24.0% versus 30.4%, p<0.05), but the difference was not significant for specimens processed after <4 h or ≥ 24 h. While overall, the culture positivity rate in the multivariate analysis did not differ between urine collected and stored in boric acid containing tubes or preservative-free tubes (OR=0.88, p=0.09), there was a decreased risk for specimens preserved with boric acid and processed between 4 and 24 h post collection when data was stratified by processing time (OR=0.80, p=0.008). 

   Biospecimens

   • Bodily Fluid - Urine

   Preservative Types

   • Other Preservative
   • None (Fresh)

   Diagnoses:

   • Not specified

   Platform:

   Analyte	Technology Platform
   Cell count/volume	Microbiological assay

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Preaquisition	Patient gender	Female Male
   Preaquisition	Patient age	Median patient age compared between positive and negative specimens
   Biospecimen Acquisition	Method of fluid acquisition	Indwelling catheter Midstream urine
   Biospecimen Acquisition	Time of biospecimen collection	Day Evening Night
   Biospecimen Preservation	Type of fixation/preservation	Boric acid None (fresh)
   Storage	Storage duration	≤4 h 4-24 h ≥24 h

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