activated protein C (APC) resistance
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Etiology
- defects in coagulation factor V
- estrogens
- elevated levels of factor VIII
Epidemiology
- accounts for 20-50% of patients presenting with venous thrombosis
- 32% of women with thrombosis while taking oral contraceptives have APC resistance
- 59% of women with DVT during pregnancy have APC resistance
- prevalence of heterozygous state is 7% in general US population
- prevalence of homozygous condition is 0.1%
Pathology
- defective degradation of factor Va by activated protein C
- poor anticoagulant response to activated protein C resulting in tendency to thrombosis
- patients with activated protein C resistance often have a 2nd risk factor for thrombosis
- estrogens are especially a problem
- 35-50 fold increased risk of thrombosis with oral contraceptives
Laboratory
Management
- avoid estrogens
- anticoagulation is NOT indicated in the absence of thrombosis
- warfarin with INR of 2-3 for single thrombosis (6 months)
- long-term warfarin with INR of 2-3 for recurrent thromboses
More general terms
Additional terms
- activated protein C (APC) resistance assay
- factor V Leiden mutation (PT 20210)
- protein C deficiency
- protein C; vitamin K-dependent protein C; anticoagulant protein C; autoprothrombin IIA; blood coagulation factor XIV; contains: vitamin K-dependent protein C light chain; vitamin K-dependent protein C heavy chain; activation peptide (PROC)
References
- ↑ Contributions from Linda Kuribayashi MD, Dept of Medicine, UCSF Fresno
- ↑ Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 724
- ↑ Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998