Regular Article
Comparison of two immunochemical assays for measuring thrombin-activatable fibrinolysis inhibitor concentration with a functional assay in patients with acute coronary syndrome

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Abstract

TAFI was measured as relative activity concentration (Pefakit) and antigen concentration (Haemochrom and Asserachrom) both acutely and during convalescence in patients suffering from acute coronary syndrome, and in a group of healthy controls. There was a rather weak but significant correlation between the activity and antigen concentrations. The results obtained by the Haemochrom method, assumed to measure the concentrations of all forms of TAFI, were lower than those by the Asserachrom method although the latter is assumed to only measure the pro-TAFI concentration. Both immunoassays gave lower results than the functional method (Pefakit). The patients in the convalescence phase showed a higher activity concentration than the healthy controls. The Asserachrom showed a higher concentration in the acute and convalescence phases of the patients compared to the controls, whereas the Haemochrom did not show any such difference. This could be related to different species of the TAFI molecule and thus different reactivity to the antibodies. Therefore the optimal choice of assay for determination of TAFI in different clinical studies is of importance. The Pefakit and Asserachrom seem to be appropriate candidates.

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Subjects

Thirty-six patients with unstable angina pectoris or non-ST-elevation myocardial infarction were included in the study. From each patient blood was sampled on four occasions: acute (sample 1, i.e. at admission to coronary care unit), 24 h after admission (sample 2), and 3 (sample 3) and 6 months (sample 4) after admission. During the course of the study two patients died and two withdrew from the study, one after the second sampling and one after the third sampling.

Patients with severe

Results

Statistically significant correlations (p < 0.01, N = 150) between the immunoassays and the functional assay were observed [r2 = 0.67 and 0.47 for Asserachrom and Haemochrom, respectively (Fig. 1). The regression functions were 0.64x + 21.6 and 0.65x + 11.7 for Asserachrom and Haemochrom, respectively. Of the three assays the Pefakit values were higher within the measurement interval than those of the immunoassays of which the Asserachrom gave higher results than the Haemochrom assay (Fig. 2). Since the

Discussion

The samples used in the present study are from a survey of hemostasis and inflammatory markers in patients with acute coronary syndrome in which e.g. the acute phase reactants fibrinogen and CRP are studied [18]. In the present report, we focus on the measurement of TAFI concentrations with assays based on different principles. The immunoassays measure the plasma concentration of total TAFI antigen or the pro-TAFI antigen, only, whereas the functional assay measures the TAFI activity

Conclusion

Our study shows that the virtual concentration and course of TAFI concentration changes during an acute coronary event and the convalescence depend on the measurement principle and method. The kinetic assay principle with high precision and easy performance speaks in favor of the chromogenic assay based on determination of TAFI activity concentration corresponding to the concentration of pro-TAFI. On the other hand, the availability of a traceable calibrator in the Asserachrom kit combined with

Acknowledgements

We are particularly grateful to Nida Soutami and Ingrid Jacobsson for their skilful performance of all analysis and Professor Margareta Blombäck for continued support and advice. We would also like to thank Barry Woodhams and Olivier Morboeuf from Diagnostica Stago for supplying Asserachrom kits and useful suggestions. The cost of one month's laboratory work (laboratory technician) was paid by Diagnostica Stago.

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Financial support for this investigation was obtained from the Heart and Lung Foundation Sweden, Stiftelsen Serafimerlasarettet, Karolinska Institutet foundation no. 176.

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