Prognostic value of risk score and urinary markers in idiopathic membranous nephropathy

Abstract

Background and objectives: Accurate prediction of prognosis may improve management of patients with idiopathic membranous nephropathy. This study compared the Toronto Risk Score and urinary low-molecular weight proteins.

Design, setting, participants, & measurements: One hundred four patients with biopsy-proven idiopathic membranous nephropathy who presented between 1995 and 2008 with a well-preserved kidney function and nephrotic range proteinuria were included. Urinary β2-microglobulin and α1-microglobulin measurements were obtained by timed standardized measurements, and the Toronto Risk Score was calculated using data obtained from medical records. The endpoint was progression, which was defined as an increase in serum creatinine > 50% or > 25% with a concentration > 135 μmol/L.

Results: Forty-nine patients showed progression. The area under the receiver-operating characteristics curve was 0.78 (95% confidence interval = 0.69-0.88) for the risk score versus 0.80 (0.71-0.89) and 0.79 (0.71-0.88) for urinary β2- and α1-microglobulin, respectively. Differences were not significant. Persistent proteinuria did not add accuracy to the Toronto Risk Score. Conversely, its accuracy was not reduced when data from the first 6 months of follow-up were used. Furthermore, a score based on GFR estimated with the six-variable Modification of Diet in Renal Disease equation, calculated in the first 6 months of follow-up, gave an area under the receiver-operating characteristics curve of 0.83 (0.74-0.92), which was not statistically different from other markers.

Conclusions: The prognostic accuracies of the Toronto Risk Score and urinary low-molecular weight proteins were not significantly different. The risk score can be calculated within 6 months of diagnosis, and a simplified risk score using estimated GFR-Modification of Diet in Renal Disease may be sufficient.

Figure 1.

Flowchart for the inclusion of patients with idiopathic membranous nephropathy in the study.

Figure 2.

Receiver-operating characteristic (ROC) curves for the Toronto Risk Score (solid), urinary β2-microglobulin (uβ2m; dots and dashes), and urinary α1-microglobulin (uα1m; long dashes). The ROC areas under the curves (AUCs) for progression were 0.78 (0.69–0.88) for the risk score, 0.80 (0.71–0.89) for uβ2m, and 0.79 (0.71–0.88) for uα1m. None of the areas under the curve differed significantly.

Figure 3.

Survival until progression by tertiles of the estimated GFR six-variable Modification of Diet in Renal Disease (eGFR-MDRD6)–based Toronto Risk Score without proteinuria calculated during the first 6 months of follow-up. The eGFR-MDRD6 risk score was calculated as the logistic function of 1.26−0.3 · ΔeGFR-MDRD6−0.05 · eGFR-MDRD6 at baseline. For the Kaplan–Meier plot, follow-up duration has been truncated at 60 months. The eGFR-MDRD6 risk score was <0.10 for the low-risk tertile (solid line), 0.10–0.30 for the medium-risk tertile (dots and dashes), and >0.30 for the highest-risk tertile (long dashes).