A new concept and a comprehensive evaluation of SYSMEX UF-1000i  flow cytometer to identify culture-negative urine specimens in patients with UTI

Abstract

Urinary tract infections (UTIs) are among the most common bacterial infections in men and urine culture is gold standard for diagnosis. Considering the high prevalence of culture-negative specimens, any method that identifies such specimens is of interest. The aim was to evaluate a new screening concept for flow cytometry analysis (FCA). The outcomes were evaluated against urine culture, uropathogen species and three conventional screening methods. A prospective, consecutive study examined 1,312 urine specimens, collected during January and February 2012. The specimens were analyzed using the Sysmex UF1000i FCA. Based on the FCA data culture negative specimens were identified in a new model by use of linear discriminant analysis (FCA-LDA). In total 1,312 patients were included. In- and outpatients represented 19.6% and 79.4%, respectively; 68.3% of the specimens originated from women. Of the 610 culture-positive specimens, Escherichia coli represented 64%, enterococci 8% and Klebsiella spp. 7%. Screening with FCA-LDA at 95% sensitivity identified 42% (552/1312) as culture negative specimens when UTI was defined according to European guidelines. The proposed screening method was either superior or similar in comparison to the three conventional screening methods. In conclusion, the proposed/suggested and new FCA-LDA screening method was superior or similar to three conventional screening methods. We recommend the proposed screening method to be used in clinic to exclude culture negative specimens, to reduce workload, costs and the turnaround time. In addition, the FCA data may add information that enhance handling and support diagnosis of patients with suspected UTI pending urine culture.

The development and validation of different decision-making tools to predict urine culture growth out of urine flow cytometry parameter

“…However, high sensitivity could be shown with our parameter too, even with a cut-off of 10 4 cfu/mL [ 15 , 16 , 31 ]. Recently, a Swedish study presented a linear discriminant analysis using bacteria and leukocytes on a log scale [ 29 ] similar to Fig 2A . The parameters were slightly different from the parameters presented in this article, which might be due to another cut-off of urine culture bacterial growth (≥10 3 cfu/mL) and the use of Sysmex UF1000i.…”

Evaluation of flow cytometry for the detection of bacteria in biological fluids

“…Particle characterization is based on forward-scatter light, side-scatter light and fluorescence. Currently, flow cytometry has been used in clinical practice to detect culture-negative urine samples based on bacterial and WBC counts [10,11]. However, it has also been increasingly used as a screening method to rapidly identify positive urine samples with high bacterial concentration to perform direct identification and antimicrobial susceptibility testing [12–14].…”

Current controversies in urinary tract infections: ICI‐RS 2017

“…The underlying infecting bacteria on urine culture may influence urine dipstick results. In their report, Monsen et al found E coli present in 65% of cultures, followed by Enterococcus (8.2%), Klebsiella (7.2%), and Staphylococcus (5.0%); urine positive for E‐coli was associated with the highest urinary leucocyte count and all culture‐positive urine samples had leucocyte counts higher than that of controls, although these results did vary between the bacteria identified.…”