What Is an Abnormal Test Strip Urinary Erythrocyte Concentration?(Technical Briefs) (Clinical Report‪)‬

Although examination of urine for red blood cells (RBCs) by automated analysis of test strips is a common, precise, and efficient method with a maximum throughput of up to 300 test strips per hour (1), the reference interval for this procedure is uncertain. Most laboratories consider a negative result as normal, based on findings in referred patients and on population studies showing that urinary tract tumors and other serious diseases are found in those with even trace amounts of blood on test strips (2-4). In two population studies, dipsticks were positive for blood in 3% of men of all ages (3) and in 13% of those over 60 years (4). A few patients with blood in their urine were found to have urothelial malignancies, but most had only a trace amount of RBCs on initial testing, with re-testing yielding intermittently positive results (3, 4); intermittently positive results may be attributable in part to variations in the methodology used because visual inspection by technicians and by patients themselves is less sensitive and less precise than semiautomated reflectance readings of urinalysis dipsticks (5). Our laboratory receives complaints from physicians about the high frequency of hematuria in their patients. We are unaware of previous studies reporting the distribution of RBC concentrations in a healthy population tested by semiautomated reflectance readings. Recent studies using a urine flow cytometer (UF-100) suggest that the number of RBCs in the urine in healthy individuals should be in the range of 10-20 cells/[micro]L with even higher numbers on dipsticks, which also measure lysed cells (6-8). In the present study we analyzed the urine of 1000 men and women of various ages seen consecutively for screening examinations and used automated analysis of the test strips to determine the reference interval.