Screening for activated protein C resistance (APCR) is used as a first-line test in the search for the factor V Leiden mutation and in the evaluation of patients with occasional or recurrent venous thromboembolism.
Activated protein C is found in plasma, is a vitamin K-dependent glycoprotein, and acts as an anticoagulant by blocking factors V and XIII. Protein C was first identified in the early 1980s. 60% of protein C is bound to a complement protein and is converted to its activated functional form by the action of a protease, and its activity is enhanced by the co-factor, protein S. Deficiency of protein C may be congenital or acquired.
Congenital deficiency of protein C is an inherited, dominant type, autosomal thrombophilia, responsible for 3-5% of cases of venous thrombosis. Congenital deficiency can manifest either as reduced levels of protein C or as resistance to protein C, despite its normal levels. Patients with homozygous deficiencies usually die as a result of thrombosis during their first year of life. Patients with heterozygous protein C deficiency often have thromboembolic episodes of venous thromboses, such as deep vein thrombosis or pulmonary embolism, at an early age.
Acquired protein C deficiency is observed in acute respiratory distress syndrome, disseminated intravascular coagulation, hemolytic uremic syndrome, liver disease, infection, postoperative conditions, vitamin K deficiency, and in patients receiving warfarin (Coumadin). Protein C deficiency is responsible for a much higher percentage of venous than arterial thrombosis.
The factor V Leiden mutation is a molecular defect in factor V, making it resistant to anticoagulant activation by protein C. It is an important cause of deep vein thrombosis as this mutation occurs in 5% of the population. The Leiden mutation is recognized by performing the resistance test for activated protein C (done by APTT time determination with and without activated protein C) and the abnormal result is confirmed by molecular DNA testing for the Leiden mutation.
What Do Pathological Values Mean?
- Increase: Diabetes, nephrotic syndrome.
- Decrease: Acute consumption (as in disseminated intravascular coagulation), congenital protein C deficiency, liver disease, vitamin K deficiency. Medications: antibiotics, asparaginase, estrogen, warfarin
Important Note
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.
