Serum complement C3 and C4 levels: prognostic factors in immunoglobulin A nephropathy

Various serum complement proteins, for example, C3 and C4, have been proposed as prognostic biomarkers of immunoglobulin A nephropathy (IgAN), but their clinical significance remains uncertain. The study aimed to identify the association of clinical data with serum complement C3 and C4 levels as possible predictive factors. A prospective cohort study at Pauls Stradins Clinical University Hospital Nephrology center included patients with histologically confirmed diagnosis of IgAN from 1st January 2020 till 20 November 2020. Daily proteinuria, serum creatinine, serum complement C3 and C4 levels were assessed. Data were analyzed using Pearson Correlation Coefficient and Mann-Whitney test by IBM SPSS Statistics 26. 37 patients (24 men, mean age 42.7 ± 10.9 years) were included in the study. Most of the patients (82%, n = 30) had normal C3 levels and C4 levels (95%, n = 35). 19% (n = 7) of patients had low C3 levels, but 5% (n = 2) of patients had high C4 levels. Median daily proteinuria was 0.38 g/24h (range 0.06 – 4.43) and median serum creatinine was 172 µmol/l (range 60 - 1514). There was no significant effect of C3 level on daily proteinuria (U = 100, p = 0.886) and serum creatinine (U = 84, p = 0.435). There was a moderate positive correlation between C4 level and serum creatinine, which was statistically significant (r = 0.329; n = 37; p = 0.047). C4 level had a tendency towards correlation with daily proteinuria (r = 0.319; n = 37; p = 0.054). The proteinuria and serum creatinine levels did not differ in the groups of patients with low or normal C3 level. The positive correlation of C4 level with serum creatinine and daily proteinuria shows that C4 may be a risk factor for IgAN progression.