Use of Sysmex UF-5000 flow cytometry in rapid diagnosis of urinary tract infection and the importance of validating carryover rates against bacterial count cut-off
Introduction. Urinary tract infections are common bacterial infections worldwide. Urine culture is the gold standard method to identify and quantify the presence or absence of bacteria in urine. Flow cytometry, which can differentiate and quantify multiple particles (including bacteria) in the urine, presents an alternative method for rapid screening to rule out bacteriuria.
Hypothesis. Adding flow cytometry to identify urine samples without bacteriuria could substantially reduce the number of urine samples that need to be cultured as well as the response time for negative results. However, the level of instrument rinsing between samples could affect sample-to-sample carryover rate, a concept given little attention in previous studies.
Aim. We aimed to evaluate urine flow cytometry as a rapid screening method to identify urine samples without significant bacterial growth, including analyses of cross-contamination and sample-to-sample carryover rate.
Methodology. We analysed 3919 urine samples by quantitative urine culture and flow cytometry screening (Sysmex UF-5000). Receiver operator characteristic (ROC) curve analyses were used to test method agreement to identify: (a) positive vs. negative culture and (b) mixed vs. pure culture. In addition, we performed carryover and cross-contamination studies.
Results. ROC curve analyses identified bacterial count (BACT ml−1) and leucocyte count (WBC µl−1) as possible predictors of bacterial growth in the total material and subpopulations, except pregnant women (n=451). This subgroup was excluded from further analyses, leaving a final 3468 urine samples. Area under the ROC curve was 0.94 (95 % CI 0.93–0.95) and 0.81 (95 % CI 0.79–0.82) for bacterial and leucocyte count, respectively. A bacterial count cut-off of 30 BACT ml−1 resulted in 95.2 % sensitivity and 91.2 % negative predictive value, resulting in approximately 30 % of urine samples that could be reported as negative without culture. Use of high-level rinse modes was necessary to ensure carryover rates <0.05 %.
Conclusion. Flow cytometry is a suitable and rapid method to rule out urine samples without significant bacterial growth. Rinses between samples should be adjusted, depending on the cut-off used, to prevent sample-to-sample carryover, whereas cross-contamination can be eliminated by the use of separate urine aliquots for flow cytometry analysis and urine culturing respectively.
This is an open-access article distributed under the terms of the Creative Commons Attribution NonCommercial License. This article was made open access via a Publish and Read agreement between the Microbiology Society and the corresponding author’s institution.
De RosaR, GrossoS, LorenziG, BruschettaG, CamporeseA. Evaluation of the new Sysmex UF-5000 fluorescence flow cytometry analyser for ruling out bacterial urinary tract infection and for prediction of Gram negative bacteria in urine cultures. Clin Chim Acta2018; 484:171–178 [View Article] [PubMed]
JolkkonenS, PaattiniemiE-L, KärpänojaP, SarkkinenH. Screening of urine samples by flow cytometry reduces the need for culture. J Clin Microbiol2010; 48:3117–3121 [View Article]
EnkoD, StelzerI, BöcklM, SchnedlWJ, MeinitzerA et al. Comparison of the reliability of Gram-negative and Gram-positive flags of the Sysmex UF-5000 with manual Gram stain and urine culture results. Clin Chem Lab Med2021; 59:619–624 [View Article] [PubMed]
MüllerM, SeidenbergR, SchuhSK, ExadaktylosAK, SchechterCB et al. The development and validation of different decision-making tools to predict urine culture growth out of urine flow cytometry parameter. PLoS One2018; 13:e0193255 [View Article]
AspevallO, HallanderH, GantV, KouriT. European guidelines for urinalysis: a collaborative document produced by European clinical microbiologists and clinical chemists under ECLM in collaboration with ESCMID. Clin Microbiol Infect2001; 7:173–178 [View Article] [PubMed]
KimSY, ParkY, KimH, KimJ, KooSH et al. Rapid screening of urinary tract infection and discrimination of gram-positive and gram-negative bacteria by automated flow cytometric analysis using Sysmex UF-5000. J Clin Microbiol2018; 56:e02004-17. [View Article] [PubMed]
Millán-LouMI, García-LechuzJM, Ruiz-AndrésMA, LópezC, AldeaMJ et al. Validation and search of the ideal cut-oSearch of the Ideal Cut-Off of the Sysmex UF-1000i® flow cytometer for the diagnosis of urinary tract infection in a tertiary hospitFlow Cytometer for the Diagnosis of Urinary Tract Infection in a Tertiary Hospital in Spain. Front Med2018; 5:92 [View Article]
EkşioğluMK, MadenciÖÇ, YücelN, ElçiA, TurhanB et al. The effectiveness of BD Vacutainer® Plus Urinalysis Preservative Tubes in preservation of urine for chemical strip analysis and particle counting. Biochem Med2016; 26:224–232 [View Article]
HiltEE, McKinleyK, PearceMM, RosenfeldAB, ZillioxMJ et al. Urine is not sterile: use of enhanced urine culture techniques to detect resident bacterial flora in the adult female bladder. J Clin Microbiol2014; 52:871–876 [View Article] [PubMed]
RobertsonJ, McGoverinC, VanholsbeeckF, SwiftS. Optimisation of the protocol for the LIVE/DEAD BacLight bacterial viability kit for rapid determination of bacterial load. Front Microbiol2019; 10:801 [View Article] [PubMed]
TavenierAH, de BoerFJ, MoshaverB, van der LeurSJCM, StegemanCA et al. Flow cytometric analysis of viable bacteria in urine samples of febrile patients at the emergency department. Cytometry B Clin Cytom2018; 94:689–695 [View Article] [PubMed]
MonsenT, RydenP. Erratum to: A new concept and a comprehensive evaluation of SYSMEX UF-1000i flow cytometer to identify culture-negative urine specimens in patients with UTI. Eur J Clin Microbiol Infect Dis2017; 36:1705 [View Article] [PubMed]
MonsenT, RydenP. A new concept and a comprehensive evaluation of SYSMEX UF-1000i flow cytometer to identify culture-negative urine specimens in patients with UTI. Eur J Clin Microbiol Infect Dis2017; 36:1691–1703 [View Article] [PubMed]
Use of Sysmex UF-5000 flow cytometry in rapid diagnosis of urinary tract infection and the importance of validating carryover rates against bacterial count cut-off