A total of 81 T2DM patients, who had kidney biopsies, were included. Indications of kidney biopsy were the sudden onset of proteinuria or nephrotic syndrome (39.5%), rapidly decreasing eGFR (37%), AGN or RPGN (12.4%), and others (11%). Of the 81 patients, 38 (46.9%) were DN alone, 28 (34.6%) were NDRD alone, and 15 (18.5%) were DN+NDRD.
The baseline clinical characteristics of all patients, as well as DN, NDRD, and DN+NDRD groups, are shown in Table 1. Mean age of all patients was 56.0 ± 13.1 years. The amount of males and females were proportional. Median duration of DM was highest in the DN group being ~10 years, with an average of five years for both NDRD and DN+NDRD group. Presence of DR was predominantly high in the DN group, accounting for 63% of those cases, with 53% having DN+NDRD, and 25% NDRD. Mean eGFR was lowest in the DN group as 31.6 ml/min/1.73m2, with 40.6 ml/min/1.73m2 in DN+NDRD, and 42 ml/min/1.73m2 in NDRD. Hematuria was found in high proportion in all three groups, but urine RBC >30 cells/HPF predominated in the NDRD group. Mean HbA1c was 7.8% for the DN group, with 7.4% in the DN+NDRD group, and 6.9% in NDRD group.
Pathological findings of NDRD
Forty-three patients were diagnosed with some type of NDRD: 28 NDRD alone and 15 DN+NDRD (Table 2). Primary membranous nephropathy, primary focal segmental glomerulosclerosis and secondary focal segmental glomerulosclerosis were the three most common lesions, each accounting for 14%. Pauci-immune glomerulonephritis, IgA nephropathy, and postinfectious glomerulonephritis were also prevalent in these groups.
Predictors associated with NDRD
Univariable and multivariable binary logistic models were used to define associations for predictors and any type of NDRD (NDRD alone or DN+NDRD). As mentioned before, four predictors (duration of DM <10 years, eGFR >30 ml/min/1.73m2, HbA1c <8 %, and absence of DR) were selected for the multivariable model due to their p value being <0.2 in the univariable model. The absence of DR showed a significant association with NDRD with the highest magnitude of association (OR 3.72; 95% CI, 1.28-10.8; p=0.02), which meant a higher likelihood of NDRD. Other predictors, which demonstrated clinically significant magnitudes of association, but without statistical significance, were duration of DM <10 years (OR 1.50; 95% CI, 0.52-4.35; p=0.46), eGFR >30 ml/min/1.73m2 (OR 2.31; 95%CI, 0.73-7.34; p=0.16), and HbA1c <8% (OR 2.82; 95% CI, 0.79-10.0; p=0.11) (Table 3). The Hosmer-Lemeshow test was performed to test goodness of fit and demonstrated a p value of 0.29. The AUC of the model was 0.75 (95% CI, 0.64-0.86).
Clinical prediction score
Within our multivariable model, the linear equation was: logodds (NDRD) = -1.75 + 0.41 (DM duration <10 years) + 0.84 (eGFR >30 ml/min/1.73m2) + 1.03 (HbA1c <8%) + 1.31 (absence of DR). In here, we used the lowest coefficients of 0.41 as a denominator, and the weighted scores were assigned as 1 for DM duration <10 years, 2 for eGFR >30 ml/min/1.73m2 and HbA1c <8%, and 3 for absence of DR.
In Table 4, we compared the estimated probability of being NDRD from the developed and optimism-adjusted models. The score ranged from 0 to 8, with a higher score associated with greater probability of NDRD. The score was divided into three categories: low probability of NDRD (score 0-2), intermediate probability (score 3-5) and high probability (score 6-8) (Figure 1). The clinical prediction score had an AUC of 0.75 in the developed model and 0.70 in the optimism-adjusted model.