FCGR1A and bacterial arthritis: The CD64-index among blood donors showed a median of 0.6 (IQR 0.5-0.8), urinary tract infection (UTI) 4.9 (2.5-7.8), flare of rheumatic arthritis (FRA) 1.0 (1.0-1.2), crystal-induced arthritis (CIA) 1.4 (0.9-1.9) and septic arthritis (SA) 2.3 (0.8-9.3).