The risk of renal complications/nephritis in patients with very high concentrations of sSIGLEC-1 was much more pronounced in European patients (OR = 1.65) compared to non-European patients (OR = 1.16; Table 2), and was maintained after adjusting for the association of sSIGLEC-1 with low C3 and C4 levels, which are predictors for renal disease (OR = 1.96, 95% CI 1.10–3.45; P = 0.021). Here, C4A is linked to nephritis.