Relationship between appearance of urinary red blood cell/white blood cell casts and the onset of renal relapse in systemic lupus erythematosus

The purpose of the study was to determine the extent to which urinary sediment findings (changes in red blood cells [RBCs], white blood cells [WBCs], and the appearance of RBC and WBC casts) predict the onset of renal relapse (defined as a specific increase in proteinuria and/or serum creatinine level) in patients with systemic lupus erythematosus (SLE). Seventeen SLE patients with biopsy-proven diffuse proliferative glomerulonephritis at initial presentation were followed prospectively for 1,129 patient-months under a study protocol. Semiquantitative urinalyses were performed at 2-month intervals during periods with little or no SLE activity and, more frequently, during periods with increased SLE activity. Each urinalysis was accompanied by a clinical evaluation and a panel of screening tests relevant to the evaluation of SLE activity. During this study, 877 semiquantitative urinalyses were performed and 43 renal relapses were observed in 14 patients. No relapse occurred in three patients. Of the renal relapses, 30 were defined as proteinuria relapses (mean baseline proteinuria increased from 0.8 ± 0.1 g/24 hr to 2.7 ± 0.3 g/24 hr; P < 0.001) and 13 were defined as serum creatinine relapses (mean baseline serum creatinine increased from 2.7 ± 0.4 mg/dL to 3.8 ± 0.5 mg/dL; P < 0.001). Red blood cell and/or WBC casts (cellular casts) were observed before or at the onset of 35 of the 43 renal relapses (sensitivity, 81%). The mean and median intervals between the appearance of cellular casts and the onset of renal relapse was 10 ± 2 weeks and 8 weeks, respectively. In patients with proteinuria ≥ 1 g/24 hr, the appearance of cellular casts accurately predicted onset of renal relapse in 24 of 25 instances (positive predictive value, 96%). In contrast, in patients with proteinuria less than 1 g/24 hr, the appearance of cellular casts accurately predicted the onset of renal relapse in only 11 of 19 instances (P < 0.01, compared with patients with proteinuria ≥ 1 g/24 hr). The appearance of cellular casts was a significantly better predictor of renal relapse than the following tests: increasing trend in urine RBCs per high-power field (P < 0.001), WBCs per high-power field (P < 0.001), dipstick testing for blood (P < 0.001), and decreasing trend in serum C3 levels (P < 0.01). We conclude that the appearance of urinary cellular casts (RBC and/or WBC casts) is a reliable predictor of SLE renal relapse, particularly in patients with proteinuria of ≥ 1.0 g/24 hr.