Differences in circulating proteins associated with COVID-19 severity were identified for FHL-1 (p<0.0001), FHR1 (p=0.0007), FHR2 (p<0.0001), FHR3 (p<0.0001), FHR4 (p=0.0006) and FHR5 (p<0.0001). Here, CFHR4 is linked to COVID-19.