A New Fully Automated Functional Assay for TAFI Determination – STA^® Stachrom^® TAFI

Abstract number: P1296

Beltran J, Combot C, Grosley M, Nicham F, Woodhams B

The clinical role of Thrombin Activatable Fibrinolysis Inhibitor (TAFI), a carboxypeptidase-B like proenzyme, remains elusive and still needs to be clearly defined. Investigations have been complicated by the lack of good functional assays and the variability of the results obtained with antigenic assays (relating to the specificity of the antibodies used in assays with the different polymorphic forms of TAFI). We report here on a new functional assay for TAFI: STA^® Stachrom^® TAFI. This fully automated colorimetric assay can be performed in 15 minutes on STA^® analyzers (Diagnostica Stago) using a two-step method: (1) Full activation of the TAFI in the sample by a thrombin-thrombomodulin reagent in the presence of a new 2 stage chromogenic substrate, specific for TAFIa, that remains coloured after the initial cleavage by TAFIa. (2) The coloured substrate product is converted to a colourless form by a second cleavage by carboxypeptidase A (active only against this coloured substrate product). The resulting colour reduction is measured at OD 405 nm. TAFI levels, as percentage activity, are read from a calibration curve prepared using a TAFI calibrator that is included in the kit. The assay is not influenced by endogenous carboxypeptidase N and has a detection limit of 5% and a measuring range up to 195%. Normal range (n= 53 healthy individuals) was 50%–150% (mean/SD: 106 ± 23%). Intra/inter assay coefficient of variation was <6% in the normal range and <8% at the 40% TAFI level. The method shows good agreement with both a specific antigenic immunoassay (n= 40, r= 0.88), minimally affected by the common TAFI polymorphisms (Asserachrom^® TAFI – Diagnostica Stago) and a commercial functional TAFI assay (n= 19, r= 0.91) (TAFI Pefakit^®– Pentapharm). This new automated STA^® Stachrom^® TAFI assay is rapid and easy to perform and will be a valuable tool to help evaluate the clinical role of TAFI.