Microtiter assay for measurement of factor XIII activity in plasma

A sensitive, reproducible and rapid quantitative microtiter assay for factor XIII activity is described. The assay is based on incorporation of a soluble amine substrate into casein attached to polystyrol microtiter plates and detection of bound substrate with a monoclonal antibody-enzyme conjugate. Defibrination of plasma samples is not required. The assay shows strong correlation with the immunologic assay for factor XIII catalytic subunit a (r = 0.94), the factor XIII dansylcadaverine assay (r = 0.83), and the factor XIII clot solubility test. Normal values detected in healthy blood donors were in the range of 74% to 117%, with a mean value of 96.9% and a median value of 97.8%; pooled normal plasma was used as a reference. Since the assay is performed in a single microtiter plate and requires few reagents and short incubation periods, it can be easily adapted for clinical use.