Development and validation of a predictive model for rapid renal function decline in early IgA nephropathy: a multicenter retrospective study

Immunoglobulin A nephropathy (IgAN) is a heterogeneous disease, and early identification of patients at high risk of rapid renal deterioration remains challenging. In this multicenter retrospective study, 483 patients with biopsy-proven IgAN at chronic kidney disease stages 1-3 were enrolled and randomly assigned to a training cohort (n = 338) and an internal validation cohort (n = 145). Rapid renal function decline was defined as a decline of at least 25% in estimated glomerular filtration rate or progression to ESRD, analyzed as a time-to-event outcome from renal biopsy (the 1-year risk was the principal metric reported). Independent predictors were identified using Cox proportional hazards regression, and a nomogram was developed and internally validated. In the training cohort, 83 patients (24.6%) reached the endpoint during follow-up (median time to event 13.6 months). Multivariable analysis showed that renal tissue Lambda light chain deposition, higher systolic blood pressure, serum chloride, blood urea nitrogen, and Oxford C score were independent risk factors, whereas higher serum complement C3 and potassium were protective factors. The nomogram showed good discrimination, with a 1-year time-dependent area under the receiver operating characteristic curve (AUC) of 0.86 (95% CI: 0.81-0.92) in the training cohort and 0.80 (95% CI: 0.69-0.91) in the validation cohort. SHAP analysis identified Lambda light chain deposition as the most influential predictor. In conclusion, we developed and internally validated a nomogram integrating clinicopathological variables to predict rapid renal function decline in early-stage IgAN, which may facilitate early risk stratification and individualized management.