PF4 and rheumatoid arthritis: The joint replacement procedure itself might be capable of triggering anti-PF4 Ab formation in both patients with osteoarthritis (OA) and those with rheumatoid arthritis (RA), which is an autoimmune disease; however, the frequency of and risks associated with anti-PF4/heparin Ab formation in RA patients who undergo joint replacement surgery without heparin exposure remain unclear.