C4A and rheumatoid arthritis: To explore the possibilities of hemolytic anemias, vasculitis, sarcoidosis, autoimmune disease, and thrombotic microangiopathy, we proceeded to get serum haptoglobin, myeloperoxidase (MPO), proteinase 3 (PR3), serum angiotensin-converting enzyme (ACE) levels, rheumatoid arthritis (RA) factor, creatine phosphokinase, C3/C4 complement levels, antinuclear antibody by immunofluorescence, and paroxysmal nocturnal hemoglobinuria (PNH) flow cytometry, all of which were negative (Table 2).