Clinical Utility of the International Risk-Prediction Tool in Japanese Patients with IgA Nephropathy

Background: Recently, International Risk-Prediction Tool (IRPT) in IgA nephropathy (IgAN) has been reported. However, the utility of IRPT remains completely unelucidated. We attempted to validate the value of IRPT in Japanese patients with IgAN. Methods: We retrospectively reviewed 145 patients (male 51.0%) with IgAN in our hospital since 2014. We collected clinical indicators, pathology, and treatment options during the observation period (mean 37 months). According to IRPT score, patients were divided into quartiles from prognostic score (PS) I to IV group. The study outcomes were end-stage kidney disease (ESKD) and estimated glomerular filtration rate (eGFR) 30% reduction. Results: At baseline, mean proteinuria and eGFR were 1.5 g/gCr and 60.0 ml/min/1.73 m2, respectively. 40.0% of patients received corticosteroid, and 36.6% underwent tonsillectomy plus corticosteroid pulse therapy (TSP). Baseline proteinuria and eGFR reduction were remarkable as IRPT-score increased (Proteinuria: PS I/II/III/IV, 0.5/1.1/1.6/3.0 g/gCr, p<0.001; eGFR: PS I/II/III/IV, 81.7/63.9/55.1/38.6 ml/min/1.73 m2, p<0.001). Degree of M1, E1, S1, and C1-2 lesions in the Oxford classification were comparable among the study groups, whereas tubulointerstitial (T1-2) lesions were significant in PS-III or PS-IV compared to PS-I or PS-II groups. Rate of patients receiving steroid therapy or TSP were comparable between the study groups. The proportion of patients who were treated with RAS inhibitor is significantly higher in PS-III or IV than in PS-I or II group. During a follow-up period, 5.6% and 15.9% of patients progressed to the ESKD and eGFR 30% reduction. Incidence of high and super high risk for dialysis proposed from Japanese Society of Nephrology (JSN) was significantly higher in PS-III or IV group compared to PS-I or II group (PS-I/II/III/IV, 2.7/33.3/61.0/83.2%, p<0.001). On Kaplan-Meier analysis, the cumulative renal survival rate to developing the ESKD or eGFR 30% reduction was significantly higher in group PS-IV than in group PS-I to II (p<0.001). However, there was no significant difference in the renal outcomes between PS I to III groups. Conclusion: IRPT is useful to assess disease severity and predict renal prognosis as well as JSN-classification. Especially, IRPT might be helpful to evaluate mid stage or advanced Japanese patients with IgAN.