Discrepancy in results between dipstick urinalysis and urine sediment microscopy

Abstract

With the advancement of urine test automation and the large-scale application of quality management policies, the source of the most crucial errors has become the pre-analytical phase. This study is an attempt to compare the results obtained from the examination of urine strips with those obtained by microscopic examination of urinary sediment, highlighting discordant results. This observational study was conducted between February and August 2019 in a private medical laboratory in Mureş County, and 2,600 urine samples were analyzed. We calculated the sensitivity, specificity, positive predictive value, negative predictive value for leukocytes, nitrites and red blood cells, taking as reference the microscopic examination of urine summary screening. Urine samples were collected from patients who presented to the laboratory. The 2,600 urine samples were analyzed using strips with 10 parameters: glucose, protein, bilirubin, urobilinogen, pH, specific density, red blood cells, nitrite, and leukocytes, and then using the microscope to examine the urinary sediment. We identified a small percentage (1.92%) of inconsistencies from the 2,600 samples of urine, between urinalysis and the microscopic examination and we identified the causes. The most common discordant results were: false-negatives for nitrite (72%), followed by false-positives results for red blood cells (22%), false-negative results for leukocytes (16%), false-negative results for red blood cells (4%) and false-positives for leukocytes (4%). The study confirmed that discrepancies appear despite the proper instruction of patients.

Keywords: dipstick urinalysis; discordant results; microscopy; pH; urine sediment.