Prognostic Value of Tubulointerstitial Lesions, Urinary N-Acetyl-β-D-Glucosaminidase, and Urinary β2-Microglobulin in Patients with Type 2 Diabetes and Biopsy-Proven Diabetic Nephropathy

Background and objectives Some biomarkers of renal tubular injury are reported to be useful for predicting renal prognosis in the early stage of diabetic nephropathy (DN). Our study compared predictions of the renal prognosis by such biomarkers and by histologic tubulointerstitial damage. Design, setting, participants, & measurements Among 210 patients with type 2 diabetes and biopsy-proven DN managed from 1985 to 2011, 149 patients with urinary N-acetyl-beta-D-glucosaminidase (NAG) and urinary beta 2-microglobulin (beta 2-MG) data at the time of renal biopsy were enrolled. The primary outcome was a decline in eGFR of >= 50% from baseline or commencement of dialysis for ESRD. Results The median follow-up period was 2.3 years (interquartile range, 1.1-5.3), and the primary outcome was noted in 94 patients. Mean eGFR was 46.3 +/- 23.2 ml/min per 1.73 m(2), and 132 patients (89%) had overt proteinuria at baseline. Cox proportional hazards analysis revealed that the association of urinary NAG and beta 2-MG with the outcome was attenuated after adjustment for known promoters of progression (+1 SD for log NAG: hazard ratio [HR], 1.14; 95% confidence interval [95% CI], 0.84 to 1.55; +1 SD for log beta 2-MG: HR, 1.23; 95% CI, 0.94 to 1.62). In contrast, the interstitial fibrosis and tubular atrophy (IFTA) score was still significantly correlated with the outcome after adjustment for the same covariates (+1 for IFIA score: HR, 2.31; 95% CI, 1.56 to 3.43). Moreover, adding the IFTA score to a model containing known progression indicators improved prediction of the outcome (increase of concordance index by 0.02; 95% CI, 0.00 to 0.05; category free net reclassification improvement by 0.54; 95% CI, 0.03 to 1.05; and relative integrated discrimination improvement by 0.07; 95% CI, -0.08 to 0.22). Conclusions Adding urinary NAG and beta 2-MG excretion to known promoters of progression did not improve prognostication, whereas adding the IFTA score did. The IFTA score may be superior to these tubulointerstitial markers for predicting the renal prognosis in advanced DN.