Eficacia y optimización de la citometría de flujo en el cribado universal de la infección del tracto urinario

Introduction

Flow cytometry has shown to be useful for ruling out urinary tract infection over the last few years. Its integration into the Microbiology Laboratories could avoid the urine culture of 60% of the samples. The aim of this study is to evaluate the usefulness of flow cytometry in the universal screening, as well as to improve its efficacy by using specific cut-off points in different groups.

Material and methods

A total of 1338 urine samples were analysed by flow cytometry (Sysmex UF-1000i), as well as a urine culture in CPS agar. Cultures with one or two pathogens and more than 10,000 CFU/ml, and special cases with less counts but just one pathogen, were considered as positive.

Results

A cut-off of > 17.1 bacteria/μl or > 29.5 leucocytes/μl resulted with a sensitivity of 95.15% and a screening yield of 32.14%. Eleven false negative were obtained, but six of them showed low counts, and another was due to Candida glabrata. On the other hand, statistically significant variations were found as regards gender and origin of the patients. The cut-off of male samples was lower than female ones. However, it remained stable in the samples from Primary Care, and it decreased notably in those from the hospital. The negative predictive value always remained over 95%.

Conclusion

Automated flow cytometry can avoid the culture of 32% of samples, even after applying tight positive criteria. In the study hospital, it would have avoided the culture of 13,705 urine samples in the year 2016. These results could improve by combining cut-off points, gender, and origin of patients.