Studies on immunological assay of vitamin K dependent factors. I. Measurement of factor VII antigen by radioimmunoassay

Area of Science:

• Biochemistry
• Immunology
• Hematology

Background:

• Factor VII is a crucial clotting protein.
• Accurate measurement of factor VII is important for diagnosing bleeding disorders and monitoring anticoagulant therapy.
• Existing methods may not fully differentiate between active and inactive forms of factor VII.

Purpose of the Study:

• To develop and validate a radioimmunoassay (RIA) for quantifying factor VII antigen (VII:Ag).
• To investigate the assay's ability to distinguish between activated factor VII (VIIa) and unactivated factor VII.
• To assess the utility of the RIA in patients with factor VII deficiency and those on warfarin therapy.

Main Methods:

• Development of a radioimmunoassay using radiolabeled factor VII, rabbit anti-factor VII serum, and goat anti-rabbit IgG serum.
• Assay validation using normal plasma and sera, including determination of sensitivity.
• Analysis of factor VII antigen levels in patients with congenital factor VII deficiency and warfarin-treated individuals.

Main Results:

• The RIA demonstrated a sensitivity of 3 X 10(-3) units/ml.
• Factor VII antigen levels in normal plasma correlated with coagulant activity but were higher in serum.
• The assay detected a 2.5-fold increase in antigen levels upon activation of factor VII to VIIa, suggesting higher affinity for VIIa.
• Detectable VII:Ag was found in two patients with severe factor VII deficiency.
• Warfarin-treated individuals showed lower VII:C compared to VII:Ag, with both normalizing within 4 weeks of cessation.

Conclusions:

• The developed RIA is a sensitive tool for measuring factor VII antigen.
• The assay can differentiate between activated and unactivated factor VII, potentially due to antibody affinity.
• The RIA aids in the diagnosis of factor VII deficiency and monitoring of warfarin therapy by assessing VII:Ag and VII:C levels.