Interlaboratory Collaboration for Optimized Screening for Urinary Tract Infection

Abstract

cAs the majority of urine samples submitted for culture yields a negative result, rapid screening that accurately predicts culture outcome benefits clinicians by reducing the time to result and improves the efficiency of the microbiological laboratory. Automated urinalysis using the IRIS Diagnostics iQ200 Elite (iQ200) analyzer permits just such a fast and large-scale screening. We aimed to predict and thus to reduce negative cultures with a screening algorithm based on iQ200 urinalysis in a tertiary university hospital. In parallel, we evaluated the performance of the iQ200 screen compared to that of Gram stain for sample quality. We screened 1,442 samples submitted for bacterial culture using the iQ200 analyzer; of these samples, 357 (24.8%) had a positive culture result. We identified the absence of microorganisms in the iQ200 screen as the strongest solitary predictor for a negative culture, with a sensitivity of 90.5% (323/357). The algorithm was further improved by performing logistic regression on leukocyte counts, which gave a cutoff of 65 leukocytes/l to obtain the desired sensitivity of >95% (95.2%; 95% confidence interval [CI], 92.5 to 97.0), a negative predictive value of 97.3% (95% CI, 95.7 to 98.3), and an anticipated culture workload reduction of 44% (95% CI, 41 to 46). Concordance between sample quality based on Gram stain and iQ200 screening was only 72%, which was probably a result of interobserver effect in evaluation of the Gram stain. In conclusion, in our setting, screening by iQ200 proved to be a safe and cost-effective means to provide faster culture results, and it has the added benefit of a more objective evaluation of sample quality. U rine cultures form a substantial part of the workload of a microbiological laboratory. They are requested even at low suspicion of urinary tract infections (UTIs), and approximately 70% of urine cultures eventually show no pathogens (1). Accurate screening for UTI before culturing the sample has multiple clinical and laboratory benefits but is hampered by the fact that sediment analysis is commonly performed outside the microbiological laboratory. However, if UTI is ruled out within hours after urine sampling, prescription of antibiotics can be withheld, thereby reducing unnecessary costs, side effects, and the risk of antibiotic resistance in microorganisms (2). If rapid screening was able to reliably predict which samples should be cultured and which need not be cultured, laboratory resources could be used more efficiently.In the last decade, automated urinalysis systems have been developed that are able to perform highly standardized and detailed quantitative urinary sediment analyses. In terms of reproducibility, these analyzers outperform manual sediment analysis (3). Automated urinalysis presents a new screening tool for UTI in the urine samples offered for culture. One of these systems is the IRIS Diagnostics iQ200 Elite (iQ200), currently marketed by Beckman Coulter Inc., which analyzes a urinary sample using flow imaging technology with auto par...

Validation and Search of the Ideal Cut-Off of the Sysmex UF-1000i® Flow Cytometer for the Diagnosis of Urinary Tract Infection in a Tertiary Hospital in Spain

“…However, this method is time consuming and often unnecessarily applied to negative samples ( 3 ). A clinically useful screening method for UTI should be rapid, inexpensive, easy to perform and must have the highest values of sensitivity and NPV ( 3 , 10 , 16 , 20 ). It is also important that there are no false-negatives, especially in immunosuppressed and elderly patients because of the severity of urinary sepsis.…”

“…The Sysmex UF-1000i and other systems such as the iQ200 classifies and quantifies the particles, including bacteria, yeasts, WBCs, and squamous epithelial cells. Nevertheless, no study has evaluated in a regressive multifactorial way the presence of epithelial cells as a NPV factor, except the study of Russcher et al ( 20 ) comparing it with Gram staining and the Q index. Muñoz-Algara et al evaluated the number of squamous epithelial cells and their relationship with contaminated urine, concluding that they can be a good predictor of contamination in urine of women of childbearing age ( 17 ).…”

“…These results could vary depending on the rate of negative cultures in the laboratory and the features of the population selected could influence it. Therefore, it is necessary to assess the screening method in different patient populations ( 20 ).…”

Prediction of urine culture results by automated urinalysis with digital flow morphology analysis

“…The number of bacteria in urine specimens obtained by Accuri C6 (BD Biosciences, San Jose, CA, US) showed good correlation with the results of urine culture when a cutoff value for urine culture positive was ≥ 10 5 CFU/mL 15 . A recent interlaboratory study exhibited that the absence of microorganisms in the iQ200 screen was the strongest solitary predictor for a negative culture result with a sensitivity of 90.5%, and higher sensitivity (95.2%) could be obtained by the algorithm based on the presence of microorganisms and the number of WBCs 16 . Another study with the iQ200 system exhibited an acceptable NPV of 97.7% and approximately 50% reduction of urine culture when using WBC ≥ 4/HPF as a cutoff in predicting urine culture results, but the PPV was only 24.5% in the same study 17 .…”

Performance of urinalysis tests and their ability in predicting results of urine cultures: a comparison between automated test strip analyser and flow cytometry in various subpopulations and types of samples

“…Previous urinalysis studies were performed in one specific population such as paediatric and women5 13 or in the whole population without subanalysis on specific subpopulation 14. A comparison of the performance of the urinalysis tests in various subpopulations is therefore difficult15 because studies need to be compared that used difference instruments 16. Despite the long history of the use of urinalysis in documenting UTIs, and despite the renewed interest in urinalysis, no studies have been published on a head-to-head comparison of urinalysis by automated test strip analyser with urinalysis by automated cell count using flow cytometry.…”