APC-resistance as measured by a Textarin time assay: comparison to the APTT-based method.

Abstract

Protein C is a major regulatory protein critical to physiologic anticoagulation. When activated, it selectively degrades the activated forms of factors V and VIII, thereby, down-regulating blood coagulation. Using an activated partial thromboplastin time (APTT) assay, Dahlback et al. recently reported that some individuals with thrombophilia show a poor in vitro anticoagulant response to activated protein C (APC-Resistance). Subsequent studies identified a point mutation in the gene for factor V as the underlying cause of APC-Resistance. The incidence of APC-Resistance in patients with recurrent thromboembolic events approaches 50%. The APC-Resistance phenotype is also present in approximately 5% of normal Caucasian subjects. In an attempt to develop a more sensitive and specific test system, we evaluated an assay based on Textarin(Pentapharm, Basel, Switzerland). Textarin, a protein fraction of Pseudonaja textilis venom (Australian Eastern Brown Snake) activates prothrombin in the presence of phospholipid (PL), factor V and calcium ions. Based on Textarin's requirement for factor V, we developed a Textarin time assay to test for APC-Resistance. We evaluated this test system in normal subjects and the following patient populations: stable orally anticoagulated, previously diagnosed factor V Leiden, and therapeutically heparinized samples. We found the Textarin assay to be a sensitive and specific test system to identify APC-Resistance. The phenotypic Textarin APC-Resistance test correlated more closely with the genotypic abnormality of factor VR506Q than the APTT-APC-Resistance test.

• Authors: L E Hoagland, D A Triplett, F Peng, L Barna
• Journal: Thrombosis research (Thromb Res) Vol. 83 Issue 5 Pg. 363-73 (Sep 01 1996) ISSN: 0049-3848 [Print] United States
• PMID: 8873345 (Publication Type: Journal Article)

Chemical References

• Anticoagulants
• Elapid Venoms
• Phospholipids
• Protein C
• factor V Leiden
• textilotoxin
• Factor V
• Prothrombin
• Heparin
• Calcium

Topics

• Anticoagulants (pharmacology)
• Blood Coagulation Tests
• Calcium (blood)
• Disease Susceptibility
• Elapid Venoms (pharmacology)
• Enzyme Activation
• Factor V (genetics, metabolism)
• Factor V Deficiency (blood, epidemiology, genetics)
• Heparin (pharmacology)
• Humans
• Incidence
• Partial Thromboplastin Time
• Phospholipids (blood)
• Point Mutation
• Polymerase Chain Reaction
• Protein C (metabolism)
• Prothrombin (drug effects)
• Reference Values
• Sensitivity and Specificity
• Thromboembolism (blood, epidemiology, etiology, prevention & control)