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.