Evaluation of Sysmex UF-1000i® flow cytometer as a screening method for asymptomatic bacteriuria and detection of Group B Streptococcus in pregnancy

Abstract

Objectives. Nowadays, the use of flow-cytometry for the screening of urine samples is extended, but appropriate cut-off points for each population group are yet to be established. The objective of this study was to evaluate the Sysmex UF-1000i® cytometer as a screening method for detection of asymptomatic bacteriuria (AB) and Group B Streptococcus (GBS) in pregnant women. Material and methods. Urine samples obtained during pregnancy between January-July 2019 were both processed with the Sysmex UF-1000i® and also cultured. Demographic data, flow-cytometry parameters and the result of the urine culture were collected. To assess the performance of the flow-cytometer for detection of AB and GBS, receiver operating characteristic (ROC) curves for the BACT/μL variable were applied. Results. A total of 33,687 urine samples were received, among which 1,443 (4.3%) belonged to pregnant women. Urine culture was positive in 82 (5.7%) samples, 1,295 (89.7%) were negative and 66 (4.6%) were considered contaminated. GBS was isolated in 69 (4.8%) patients and 46 (66.7%) with a microbial count below 10E4 CFU/mL. For AB detection, the cut-off point of 550 BACT/μL yielded a sensitivity of 91.5%, a negative predictive value of 99.3% and could avoid culturing 74.1% of the samples. No cut-off value could be established for GBS detection. Conclusions. Although the Sysmex UF-1000i® system is a valid screening method for the AB detection in pregnant population, it is not useful for the identification of GBS bacteriuria in our area. Therefore, the conventional urine culture is still required during pregnancy.