Serum immunoglobulin G provides early risk prediction in immunoglobulin A nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is a common primary glomerular disease that potentially leads to renal failure, risk prediction of declining kidney function is crucial for early clinical management. Immunoglobulin G (IgG) is an important constituent of the immune system and serves as the preferred therapeutic target in human autoimmune diseases. However, its role in the progression of IgAN is unclear. From May 2009 to April 2014, 455 patients diagnosed with IgAN at the Second Xiangya Hospital were enrolled in this study; the median follow-up was 42.2 months. All subjects were divided into four groups according to IgG level quartiles. The study endpoint was end-stage renal disease (ESRD) or an irreversible 50% estimated glomerular filtration rate (eGFR) reduction. Clinical data and pathological features of renal biopsy specimens were collected. Among IgAN patients, serum IgG levels were directly correlated with the levels of serum albumin and serum IgA but reversely correlated with body weight, systolic blood pressure, and serum creatinine and cholesterol levels. According to stratified analysis of serum IgG, the proportions of composite renal endpoints among the enrolled IgAN patients in the serum IgG concentration subgroups 1 (<7.86), 2 (7.86–10.30), 3 (10.31–12.70), and 4 (>12.71 g/l) were 9.6%, 9.2%, 3.7%, and 3.7% respectively. Importantly, cumulative renal survival rates were significantly higher in the patients with increased serum IgG (p = 0.0114). Serum IgG was also predictive of renal survival, with an HR of 0.745 (95% CI, 0.614 to 0.905, p = 0.003) after adjusting for significant factors in the univariate Cox regression and an HR of 0.871 (95% CI, 0.780 to 0.973, p = 0.014) adjusting for traditional risk factors of IgAN. These findings demonstrate that a decreased serum IgG level at the time of renal biopsy is independently associated with a poor renal outcome in IgAN patients.