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activated protein C (APC) resistance

Etiology: 1) defects in coagulation factor V - factor V Leiden mutation 2) estrogens 3) elevated levels of factor VIII Pathology: 1) defective degradation of factor Va by activated protein C 2) poor anticoagulant response to activated protein C resulting in tendency to thrombosis 3) patients with activated protein C resistance often have a 2nd risk factor for thrombosis 4) estrogens are especially a problem - 35-50 fold increased risk of thrombosis with oral contraceptives Epidemiology: 1) accounts for 20-50% of patients presenting with venous thrombosis a) 32% of women with thrombosis while taking oral contraceptives have APC resistance b) 59% of women with DVT during pregnancy have APC resistance 2) prevalence of heterozygous state is 7% in general US population 3) prevalence of homozygous condition is 0.1% Laboratory: 1) protein C assay a) functional assay (difficult to interpret in patients on warfarin) b) 2nd generation APC resistance assay is useful in patients on warfarin 2) coagulation factor V Leiden mutation by PCR 3) activated protein C resistance assay Management: 1) avoid estrogens 2) anticoagulation is NOT indicated in the absence of thrombosis 3) warfarin with INR of 2-3 for single thrombosis (6 months) 4) long-term warfarin with INR of 2-3 for recurrent thromboses

Related

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)

General

hypercoagulability

Database Correlations

OMIM 188055

References

  1. Contributions from Linda Kuribayashi MD, Dept of Medicine, UCSF Fresno
  2. Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 724
  3. Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998