Assessment of Interobserver Reliability of Nephrologist Examination of Urine Sediment

Abstract

Importance: Urine sediment microscopy is commonly performed during the evaluation of kidney disease. Interobserver reliability of nephrologists' urine sediment examination has not been well studied.

Objective: Assess interobserver reliability of the urine sediment examination.

Design, setting, and participants: In this diagnostic test study, urine samples were prospectively collected from a convenience sample of adult patients from an academic hospital in the United States undergoing kidney biopsy from July 11, 2018, to March 20, 2019. Digital images and videos of urine sediment findings were captured using a bright-field microscope. These images and videos along with urine dipstick results were incorporated in online surveys and sent to expert nephrologists at 15 US teaching hospitals. They were asked to identify individual sediment findings and the most likely underlying disease process.

Exposures: Urine dipstick results and urine sediment images from patients undergoing native kidney biopsy.

Main outcomes and measures: Interobserver reliability of urine sediment microscopy findings estimated by overall percent agreement and Fleiss κ coefficients. Secondary outcomes included concordance of diagnoses suspected by nephrologists with corresponding kidney biopsy results.

Results: In total, 10 surveys from 10 patients containing 76 study questions on individual features were sent to 21 nephrologists, 14 (67%) of whom completed them all. Their combined 1064 responses were analyzed. Overall percent agreement for casts was an estimated 59% (95% CI, 50%-69%), κ = 0.52 (95% CI, 0.42-0.62). For other sediment findings, overall percent agreement was an estimated 69% (95% CI, 61%-77%), κ = 0.65 (95% CI, 0.56-0.73). The κ estimates ranged from 0.13 (95% CI, 0.10-0.17) for mixed cellular casts to 0.90 (95% CI, 0.87-0.94) for squamous epithelial cells.

Conclusions and relevance: In this study, substantial variability occurred in the interpretation of urine sediment findings, even among expert nephrologists. Educational or technological innovations may help improve the urine sediment as a diagnostic tool.

Figure 1.. Example Digital Images Reviewed by Nephrologists

Images were obtained at high power (40 × objective). Arrowheads indicate findings of interest that nephrologists were asked to identify. Their responses (No.) are shown above each image. The inset of panel B is the same field under polarized light.

Figure 2.. Distribution of Responses

For each type of response listed, the number of times that it was chosen by the reviewers while representing the most common answer to a given image is shown in gray. In total, the 14 reviewers provided 1064 responses to the questions asking them to identify individual sediment findings included in this analysis. KTEC indicates kidney tubular epithelial cell; RBC, red blood cell; and WBC, white blood cell.

Figure 3.. Chord Diagram Depicting Disease Process Suspected Based on Urinalysis Findings

The chord diagram depicts the underlying disease process suspected by 14 nephrologists after their review of urinalysis data and urine sediment images from 10 patients undergoing kidney biopsy. Individual cases listed from 1 to 10 on the left side of the diagram correspond to the listing in Table 2, in which the clinicopathologic diagnoses made after kidney biopsy are presented. The width of each chord is determined by the number of nephrologists who gave the same answer. The total number of times each diagnostic category was chosen during the course of the study is also shown next to the segments representing the individual categories on the right side of the figure. AIN indicates acute interstitial nephritis; ATN, acute tubular necrosis; GN, glomerulonephritis; and UTI, urinary tract infection.