High false positive rate of white blood cells in urine samples of pregnant women may be caused by epithelial cells being misclassified by the sysmex UF‐1000i urine flow cytometer

BACKGROUND: The UF‐1000i has been widely used in screening urinary sediments. However, the interference factor of the UF‐1000i in the screening urinary sediments of pregnant women has not been reported. The aim of the study was to demonstrate that epithelial cells (ECs) cause a high false positive rate of white blood cells (WBCs) by the UF‐1000i in pregnant women. METHODS: Urine samples were collected from 207 pregnant women. All samples were measured by the UF‐1000i and a microscopic method. RESULTS: The areas under the curve (AUC) for WBC and EC counts were 0.837 (95% CI, 0.773–0.901) and 0.844 (95% CI, 0.785–0.903), respectively. The positive rates of the WBC and EC were 73.43% and 37.20%, respectively, by the UF‐1000i, and they were 19.32% and 72.95% by the microscopic method. The positive predictive value, negative predictive value, false positive rates, and false negative rates by the UF‐1000i were for WBC 25.66%, 98.18%, 74.34%, and 1.82%, respectively, and for EC they were 96.1%, 40.77%, 3.9%, and 59.23%, respectively. The coefficient of correlation R value was 0.503 (P < 0.01) between WBC by UF‐1000i and EC by the microscopic method in WBC false positive samples. CONCLUSIONS: EC could be an interference factor for the UF‐1000i in screening urinary WBC of pregnant women, and the high false positive rate for WBC may be caused by ECs being misclassified as WBCs by the UF‐1000i. © 2018 The Authors. Cytometry Part B: Clinical Cytometry published by Wiley Periodicals, Inc. on behalf of International Clinical Cytometry Society.