Clinical Significance of Combined IgM and C3 Staining in Primary IgA Nephropathy

Background We aimed to investigate the clinical significance of combined glomerular IgM and C3 staining and renal outcome in adult IgA nephropathy (IgAN). Materials and Methods This retrospective study encompassed 69 adult patients with IgAN. The demographic and clinical data, including sex, age, diastolic blood pressure (DBP), systolic blood pressure (SBP), 24-hour urinary total protein (24hUP), WBCs, serum hemoglobin (Hb), serum platelets (PLT), serum creatinine (Scr), blood uric nitrogen (BUN), estimated glomerular filtration rate (eGFR), serum albumin (ALB), uric acid (UA), total cholesterol (CHO), triglyceride (TG), IgA, IgG, IgM, and complement 3 and 4 (C3 and C4) were evaluated at baseline. Kidney biopsy was categorized using the Oxford classification, along with the Mesangial hypercellularity, endocapillary hypercellularity, segmental glomerulosclerosis, tubular atrophy/interstitial fibrosis, glomerular crescent, (MEST-C) score. The patients were divided into IgM-positive (IgM + ) and-negative (IgM - ) groups for analysis. Further, they were divided into four groups by glomerular IgM and C3 staining: IgM-positive C3-positive (IgM + C3 + ) staining group, IgM-positive C3-negative (IgM + C3 - ) staining group, IgM-negative C3-positive (IgM - C3 + ) staining group, and IgM-negative C3-negative (IgM - C3 - ) staining group. The hard renal endpoint was the onset of end-stage kidney disease (ESKD) within the follow-up period. Results The IgM + group (n=47, 68%) had significantly higher levels of SBP, Scr, BUN, IgM, TG, 24hUP, tubular atrophy, and vessel hyaline change. Further analysis indicated that 43 (62.3%) patients had combined mesangial IgM and C3 deposition (IgM + C3 + staining group). Compared with the other three groups, patients with combined IgM and C3 deposition had higher levels of DBP, SBP, Scr, BUN, IgM, TG, and 24-hour urine protein (24hUP), as well as tubular atrophy. We observed that the IgM + C3 + group had a higher prevalence of renal dysfunction compared to the other groups. Conclusion IgM positivity in patients with IgA showed a worse renal outcome. IgM + C3 + staining in patients with IgAN experienced a higher renal dysfunction prevalence.