AN ENZYME-LINKED IMMUNOSORPTION ASSAY FOR TISSUE FACTOR PATHWAY INHIBITOR

An assay for the quantification of full-length and carboxy-terminus tr uncated tissue factor pathway inhibitor (TFPI) has been developed. The assay is a classical two-antibody sandwich assay with a monoclonal ca pture antibody directed against the third Kunitz-type domain of human TFPI and a polyclonal rabbit peroxidase-labelled anti-human TFPI detec ting antibody. The assay is sensitive to full-length and carboxy-termi nus truncated TFPI with intact third Kunitz-type domain, but not to tw o-domain TFPI. TFPI associated with lipoproteins is not or only sparse ly detected and TFPI in complex with factor Xa only partially measured . The assay gives linear reference curves in the dose range of 5 to 10 0 ng/ml in a double logarithmic plot. The normal range assessed from a nalyses on citrated plasma from 81 normal human donors is 7.8 to 26.0 ng/ml (average +/- 2 SD, log-normal distribution). There is no statist ically significant difference between TFPI levels measured in 10 fasti ng and 10 non-fasting individuals. The reproducibility of the assay is about 5.6-5.9% (relative standard error) and the within-days and betw een-days reproducibilities are 4.7-5.1% and 5.9-8.5%, respectively. Th e assay is in very good agreement with a commercial ELISA assay recent ly marketed. A robust, reproducible and convenient ELISA assay for the determination of full-length and three-domain TFPI has been developed . (C) 1997 Elsevier Science Ltd.