Urine Sediment Examination: Comparison Between Laboratory-Performed Versus Nephrologist-Performed Microscopy and Accuracy in Predicting Pathologic Diagnosis in Patients with Acute Kidney Injury.

Abstract

Automated urine technology is becoming standard for urinalysis microscopy. We sought to compare the urine sediment analysis performed by nephrologist to the analysis performed by the laboratory. When available, we also compared the suggested diagnosis per nephrologists' sediment analysis to the biopsy diagnosis. We identified patients with AKI that had urine microscopy with sediment analysis performed by the laboratory (Laboratory-UrSA) and by a nephrologist (Nephrologist-UrSA) within 72 hours of each other. We collected data to determine the following: number of RBCs and WBCs per HPF, presence and type of casts per LPF, and presence of dysmorphic RBCs. We evaluated agreement between the Laboratory-UrSA and the Nephrologist-UrSA using cross tabulation and Kappa statistic. When available, we categorized the nephrologist sediment findings into four categories: (1) bland, (2) suggestive of acute tubular injury (ATI), (3) suggestive of glomerulonephritis (GN), and (4) suggestive of acute interstitial nephritis (AIN). In a group of patients with kidney biopsy within thirty days of the Nephrologist-UrSA, we assessed agreement between the nephrologist diagnosis and the biopsy diagnosis. We included 387 patients with both Laboratory-UrSA and Nephrologist-UrSA. The agreement was moderate for presence of RBCs (Kappa 0.46, 95% CI: 0.37, 0.55), fair for WBCs (Kappa 0.36, 95% CI: 0.27, 0.45). There was no agreement for casts (Kappa 0.026, 95% CI: -0.04, 0.07). Eighteen dysmorphic RBCs were detected on Nephrologist-UrSA compared to zero on Laboratory-UrSA. Among the 33 patients with kidney biopsy, 100% ATI and 100% GN suggested per Nephrologist-UrSA were confirmed on the biopsy. Of the 5 patients with bland sediment on the Nephrologist-UrSA, 40% showed ATI pathologically while the other 60% demonstrated GN. A nephrologist is more likely to recognize the presence of pathologic casts and dysmorphic RBCs. Correct identification of these casts carries important diagnostic and prognostic value when evaluating kidney disease.