ACTIVATED PROTEIN C RESISTANCE: WHAT IS ACTIVATED PROTEIN C RESISTANCE?
Definition: What is "Activated Protein C Resistance"?
Activated protein C resistance is a hemostatic disease which is characterized by a reduced anticoagulant response to APC or activated protein C. The result is a heightened risk of venous thrombosis. The activated protein C resistance or APCr was first studied & reported by Dahlback in 1993. Activated protein C with protein S as its co-factor degrades Factor VIIIa & Factor Va. Activated protein C resistance is the failure of protein C to cleave Factor VIIIa and/or Factor Va. This permits for a longer extent of thrombin generation & could proceed to the hypercoabulable phase. The most common form of hereditary resistance to activated protein C is Factor V Leiden. Acquired types occur together with elevated concentrations of Factor VIII. It has been evaluated that up to 64% of people who are afflicted with venous thromboembolism could also have activated protein C resistance.
Symptoms & Signs
The clinical symptoms include: thrombosis; placental abruption; preeclampsia; intrauterine growth impairment; & stillbirths. These symptoms are highly different in APC resistant people. Some patients do not get thrombosis while a few others suffer from recurring acute thrombotic incidents. The homozygosity for the mutation on Leiden provides a greater risk of thrombosis when compared to heterozygosity. The risk of getting thrombosis is heightened by the other co-existent risk factors that are acquired or protein deficiencies. Other risk factors that are genetic for thrombosis also include lack of protein C, antithrombin III & protein S. Factor II gene mutations & the MTHFR or homocysteine related methylene tetrahydrafolate polymorphism are also factors that increase the occurrence of thrombosis. The general risk factors that are acquired are pregnancy, trauma, contraceptive use, the presence of antibodies that are antiphospholipids & surgery.
Before any type of APCr test can be given, it is necessary to diagnose all the factors which determine the risk of thrombosis.
Patients who acquire venous thrombosis for the first time & also FVL mutation (with no other thrombotic risks) could have the anticoagulant therapy hampered. In case a second case occurs, it is recommended that an indefinite anticoagulant therapy be given. Those individuals with venous thrombosis, a second acquired or inborn risk factor & FVL commonly require anticoagulation that is indefinite. Asymptomatic FVL carriers should be anticoagulated for surgery. Anticoagulation among asymptomatic carriers who are pregnant is presently not recommended. As is practiced, the regiments of treatments might need individualization.