The Feasibility of Japanese Histological Grade Classification for Predicting Renal Function Deterioration among Taiwanese Individuals with IgA Nephropathy

We aimed to validate the Japanese histological grading classification (JHGC) in our population of IgA immunoglobulin (IgAN) cases.

We conducted a retrospective cohort study at Taichung Veterans General Hospital in Taiwan from January 2011 to December 2023. The process involved assessing JHGC's clinical, histological, and merged grading system. Composite renal outcomes based on glomerular filtrate rate (eGFR) were considered.

The study included 359 IgAN by renal biopsies. Kidney function at the time of biopsy was suboptimal, with average SCr of 1.3 mg/dL, eGFR of 54.0 mL/min/1.732 m², and urine protein-creatinine ratio (UPCR) of 1.2 mg/mg. JHGC effectively identified different severity levels of histological and clinical aspects in Taiwanese IgAN. Initial 4-histological classification showed significantly higher MEST-C scores (p < 0.001). Merging grade III and IV was reasonable in Japanese and Taiwanese populations. The clinical grading system (3C) was associated with histological status and proteinuria, but there was no significant trend with SCr, eGFR, and blood urea nitrogen. Significant differences were found among the three groups (log-rank p < 0.01), but C-grade I and II lacked significant difference in long-term renal outcomes. We separated UPCR < 0.5 mg/mg into two groups: eGFR≥ and <60 mL/min/1.732 m². The new grading system effectively differentiated risk factors for renal outcomes (log-rank p < 0.01), suggesting the need for separation in Taiwanese IgAN.

Our study externally validated JHGC in non-Japanese IgAN. Despite applicability to our population, we recommend a new classification specifically for Taiwanese IgAN patients with increased case numbers in eGFR ≥ 60 mL/min/1.732 m² and UPCR < 0.5 g/day group.