CFP and spondyloarthropathy: Patients with connective tissue diseases (CTD, n = 10), polymyalgia rheumatica (PR, n = 31), rheumatoid arthritis (RA, n = 38), spondyloarthritis (SPA, n = 40) and systemic sclerosis (SSc, n = 16) showed no discriminable properdin detection compared to the positive control (means were 94%, 99%, 95%, 103% and 100%, respectively).