Interobserver Reliability of Urine Sediment Interpretation

Background and objectives: Urine sediment interpretation is frequently used in the evaluation of patients with kidney disease. There has been no systematic evaluation of the reliability of this diagnostic maneuver. Design, setting, participants, & measurements: Digital photographs of urine sediment images were acquired from 165 consecutive patients being evaluated by the nephrology consultation service at a tertiary care hospital. Urine sediment images of 100 patients were randomly selected; 86 patients had images that were deemed to be of sufficient quality, and one image per patient was chosen for inclusion in an internet-based questionnaire. For each image, the presence or absence of 14 potential urinary structures was ascertained. Ten nephrologists (senior readers [n = 3]: > 10 yr of experience; intermediate readers [n = 3]: 1 to 10 yr of experience; and junior readers [n = 4]: first year of practice) completed the questionnaire. For each urinary structure, we measured the rate of complete agreement among the readers as well as the kappa statistic as a marker of agreement beyond chance. Results: Unanimous agreement was highest (79.1%) regarding the presence of broad and fatty casts and poorest (31.4%) for the identification of dysmorphic red blood cells and white blood cells. Interobserver agreement was best for squamous epithelial cells (kappa = 0.54) and hyaline casts (kappa = 0.52) and worst for transitional epithelial cells (kappa = 0.14) and fatty casts (kappa = 0.06). When assessed within strata of physician experience, interobserver agreement was not associated with seniority. Conclusions: Nephrologists achieved slight to moderate agreement in the identification of structures that are commonly observed in the urine sediment.