Modified APC-resistance test: variable ratios with respect to source of factor V-deficient plasma

Area of Science:

• Hematology
• Thrombosis Research
• Clinical Chemistry

Background:

• Factor V Leiden (FV-Leiden) mutation causes APC-resistance, a major venous thrombosis risk factor in Caucasians.
• The activated partial thromboplastin time (APTT) based APC ratio is a common screening method.
• Standard APC ratio testing is unreliable in patients on oral anticoagulants due to vitamin K-dependent clotting factor interference.

Purpose of the Study:

• To evaluate a modified APC-sensitivity assay using FV-deficient plasma for screening APC-resistance.
• To assess the assay's applicability in patients on warfarin therapy.
• To investigate the impact of different commercial FV-deficient plasma sources on APC ratio results.

Main Methods:

• A modified APC-sensitivity assay was developed, involving dilution of test plasma with FV-deficient plasma.
• The modified assay was tested on normal individuals, FV-Leiden positive individuals, and patients on warfarin.
• APC ratios from the modified assay were compared to those from the original method, using FV-deficient plasma from various commercial sources.

Main Results:

• APC ratios determined by the modified method differed significantly from the original method across all tested groups.
• The modified method successfully identified APC-resistance in patients on warfarin therapy.
• Significant variations in APC ratios were observed depending on the commercial source of the FV-deficient plasma used.

Conclusions:

• The modified APC-sensitivity assay using FV-deficient plasma is a viable method for detecting APC-resistance in patients on warfarin and other individuals.
• Clinicians must be aware that APC ratios obtained with the modified method are not directly comparable to the original method's results.
• The choice of commercial FV-deficient plasma source can influence APC ratio outcomes in the modified assay, necessitating careful consideration and standardization.