C3 and chronic kidney disease: To explore the association between serum Gd-IgA1, IgA, IgA/C3 levels, and CKD progression based on the eGFR, the patients with IgAN were divided into two groups: “CKD progression” included patients with a 25% reduction in eGFR or a decline in the eGFR category from the value determined at the time of renal biopsy, while “CKD non-progression” included the remaining patients who did not meet the criteria for progression.