FEMALE GENDER AND RESISTANCE TO ACTIVATED PROTEIN-C (FV-Q(506)) AS POTENTIAL RISK-FACTORS FOR THROMBOSIS AFTER ELECTIVE HIP-ARTHROPLASTY

Resistance to activated protein C (APC) caused by the R(506)Q mutation in factor V is the most common inherited risk factor for venous throm bosis. To elucidate whether APC-resistance is a risk factor for venous thrombosis after elective total hip replacement, the association betw een APC-resistance (presence of FV:Q(506) allele) and postoperative th rombosis was investigated in patients (n = 198) randomised to received short (during hospitalisation, n = 100) or prolonged prophylaxis (thr ee weeks after hospitalisation, n = 98) with low molecular weight hepa rin (LMWH). Among APC-resistant individuals receiving short prophylaxi s, 7/10 developed thrombosis as compared to 2/12 receiving long prophy laxis (p < 0.0179). Odds ratio for association between APC-resistance and thrombosis in the short prophylaxis group was 4.2 (CI 95% 1.02 - 1 7.5) (p < 0.0465). Among those receiving prolonged prophylaxis, there was no increased incidence of thrombosis associated with APC-resistanc e. Two unexpected. observations were made. One was that APC-resistance was much more common in women (19/109) than in men (3/89) (p < 0.001) . The other was that even women without APC-resistance were much more thrombosis-prone than men. Thus, 24/48 of women with normal FV genotyp e and short prophylaxis developed thrombosis vs 8/42 among men, p = 0. 002. The increased risk of thrombosis associated with female gender an d APC-resistance was neutralised by the prolonged treatment. In conclu sion, among patients receiving short prophylaxis, female gender was fo und to be a strong risk factor for venous thrombosis. Even though APC- resistance appeared to be a risk factor for postoperative thrombosis, the uneven distribution of APC-resistance. between men and women, take n together with the increased risk of thrombosis among women, preclude d valid conclusions to be drawn about the association between APC-resi stance and an increased risk of thrombosis. Our results suggest that p rolonged prophylaxis with LMWH after hip surgery is more important for women than for men.