PF4 and rheumatoid arthritis: The seroconversion of anti-PF4/heparin Ab did not affect the occurrences of postoperative DVT (anti-PF4/heparin Ab +21.1 % vs anti-PF4/heparin Ab –23.6 %) or bleeding (anti-PF4/heparin Ab +5.3 % vs anti-PF4/heparin Ab –5.6 %) in RA patients.