Flow Cytometry Utilized to Screen Urine Specimens

Screening urine by flow cytometry would minimize the number of specimens cultured yet ensuring that all true positives were cultured.The method was used in a study at the University of Manitoba, (Winnipeg, MB, Canada) where 2,496 urine specimens were screened and cultured. Urine specimens were cultured on nonselective differentiation medium and analyzed by the UF-1000i urine fluorescence-flow cytometer. Various combinations of WBC/bacterial counts were assessed as screening criteria and correlated with significant growth on the culture medium.

The urine samples were cultured on CHROMaga Orientation medium (Becton Dickinson, Mississauga, ON, Canada). Of the 2,496 samples of urine cultured, 75% were midstream urine and 25% were catheterized urine. Of the midstream urine specimens, 27.3% grew significant pathogens (SIGs), 68.6% showed nonsignificant growth (NSIG), whereas 4.1% had growth suggestive of possible contamination (PCON). Of the 622 catheter urine samples cultured, 34.2% grew SIGs, 61.2% showed NSIG, whereas 4.6% showed PCON.

The flow cytometer, UF-1000i, is a product of Sysmex (Mississauga, ON, Canada) and it was provided for this study by bioMérieux, (St Laurent, QC, Canada).

A bacterial count equal to or greater than 20 from the flow cytometer (UF) gave an overall screening sensitivity of 92.6%, allowing 35% of specimens to be screened out and not cultured. The sensitivity was 99.2% and 85.0% for Gram-negative and Gram-positive organisms, respectively, using the same bacterial count. There were 27 patients with UF false-negative results, but only four had urinary tract infections and were treated using appropriate antibiotics. The authors concluded that the study indicated that UF was a simple, rapid, and reliable method for urine screening when the bacterial count of above 19 was used as the sole screening criterion. The study was published in the February 2010 issue of Diagnostic Microbiology and Infectious Disease.

Related Links:
University of Manitoba
BectonDickinson
Sysmex
bioMérieux