Improved distinction of factor V wild-type and factor V Leiden using a novel prothrombin-based activated protein C resistance assay

• Published in: American journal of clinical pathology Vol. 122; no. 6; pp. 836 - 842
• Main Authors: WILMER, Marianne, STOCKER, Christoph, BÜHLER, Beatrice, CONELL, Brigitte, CALATZIS, Andreas
• Format: Journal Article
• Language: English
• Published: Chicago, IL American Society of Clinical Pathologists 01.12.2004
• Subjects: Biological and medical sciences; Blood Coagulation Tests - methods; Factor V - analysis; Factor V - genetics; Factor V Deficiency - blood; Hematologic and hematopoietic diseases; Humans; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Mutation; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Platelet diseases and coagulopathies; Protein C - metabolism; Prothrombin - metabolism; Sensitivity and Specificity; Antiphospholipid antibody syndrome; Factor V Leiden; Russell viper venom-factor V; Cardiovascular disease; Autoimmune disease; Hemopathy; Noscarin; Wild type; Antiphospholipid antibodies; Ophidia; Vascular disease; Assay; Factor V; Resistance; Thrombophilia; Vertebrata; Anatomic pathology; Platelet; Venom; Prothrombin; Activated protein C resistance; Reptilia
• ISSN: 0002-9173; 1943-7722
• DOI: 10.1309/T8AVVH7QWGL0QTF5

A new prothrombin-based activated protein C resistance (APC-R) test is described. In this method, the patient sample is prediluted in a plasma depleted of factor V (FV). A reagent containing APC and a specific activator of FV is added. After an incubation period, clotting is initiated by the addition of the FV-dependent prothrombin activator Noscarin. We analyzed 703 samples from patients undergoing thrombophilia screening. By using a predefined cutoff ratio of 2.5, 100% sensitivity and specificity for the detection of a factor V Leiden (FVL) mutation was found. With a cutoff ratio of 1.2, a complete but narrow distinction of FVL heterozygous (n = 192) and FVL homozygous samples (n = 27) was determined. No interference by the international normalized ratio, activated partial thromboplastin time (aPTT), protein S activity, fibrinogen and factor VIII (FVIII) levels, or lupus anticoagulant ratio was detected. The new prothrombin-based APC-R assay provides improved distinction of FV wild-type and FVL carriers compared with the aPTT-based method. By the use of an FV-dependent prothrombin activator, the assay is not influenced by FVIII concentration or lupus anticoagulants.