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

KEY POINTS: A nephrologist is more likely to recognize the presence of pathologic casts and dysmorphic red blood cells. Nephrologist-performed urine sediment analysis is also highly accurate in diagnosing acute tubular injury or glomerulonephritis when compared with kidney biopsy. INTRODUCTION: Automated urine technology is becoming the standard for urinalysis microscopy. We sought to compare urine sediment analysis performed by a nephrologist with the analysis performed by the laboratory. When available, we also compared the suggested diagnosis per nephrologists' sediment analysis with the biopsy diagnosis. METHODS: We identified patients with AKI who 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 red blood cells (RBCs) and white blood cells (WBCs) per high-power field, presence and types of casts per low-power field, and presence of dysmorphic RBCs. We evaluated agreement between the Laboratory-UrSA and the Nephrologist-UrSA using cross-tabulation and the 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 30 days of the Nephrologist-UrSA, we assessed agreement between the nephrologist diagnosis and the biopsy diagnosis. RESULTS: We included 387 patients with both Laboratory-UrSA and Nephrologist-UrSA. The agreement was moderate for the presence of RBCs (Kappa, 0.46; 95% CI, 0.37 to 0.55) and fair for WBCs (Kappa, 0.36; 95% CI, 0.27 to 0.45). There was no agreement for casts (Kappa, 0.026; 95% CI, −0.04 to 0.07). Eighteen dysmorphic RBCs were detected on Nephrologist-UrSA compared with 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 five patients with bland sediment on the Nephrologist-UrSA, 40% showed ATI pathologically while the other 60% demonstrated GN. CONCLUSION: 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.