Serum levels of galactose-deficient IgA are elevated in patients with IgA nephropathy but do not correlate to disease activity or progression

INTRODUCTION: IgA nephropathy (IgAN) is the most common glomerulonephritis globally. Because of the heterogeneity of the disease prognostic biomarkers are highly needed. AIM: To investigate associations between galactose-deficient IgA1 (Gd-IgA1) concentrations in plasma and urine and disease activity and progression in patients with IgAN. METHODS: Serum and urine samples were collected at the time of kidney biopsy (baseline) in patients with IgAN (n = 40) and analysed for Gd-IgA1. Patients with chronic kidney disease (CKD) without IgAN (n = 21) and healthy controls (n = 19) were examined as controls. In 19 patients with IgAN, analyses of Gd-IgA1 were repeated after a median follow up time of approximately 10 years. RESULTS: Serum Gd-IgA1 and Gd-IgA1:IgA were significantly elevated at the time of kidney biopsy in patients with IgAN compared to patients with non-IgAN CKD and healthy controls (p < 0.001). Urinary Gd-IgA1:creatinine was significantly elevated in patients with IgAN compared to patients with non-IgAN CKD. Neither serum Gd-IgA1, nor serum Gd-IgA1:IgA, correlated significantly to estimated GFR, urine albumin:creatinine (UACR), or blood pressure, at baseline. Serum Gd-IgA1 and Gd-IgA1:IgA at time of biopsy did not correlate significantly to annual changes in eGFR or UACR during follow up. In patients with IgAN, serum Gd-IgA1 decreased significantly over time during approximately 10 years of follow up (Δ-20 ± 85%, p = 0.027). Urinary Gd-IgA1:creatinine showed a strong positive correlation to UACR in patients with IgAN and likely reflected unspecific glomerular barrier injury. CONCLUSION: Although serum Gd-IgA1 and the Gd-IgA1:IgA ratio were significantly elevated in patients with IgAN at the time of kidney biopsy they were not related to disease activity or progression in this patient cohort.