A-187 The A2M assay of Diagam on the DxC500AU from Beckman Coulter.

Abstract

Alpha-2-macroglobulin (A2M) is a high-molecular-weight plasma protease inhibitor (725 kDa) mainly synthesized by hepatocytes. It binds numerous growth factors, cytokines, and hormones and participates in the regulation of fibrinolytic/coagulation, kallikrein, and complement cascades, as well as in the transport of molecules such as growth hormone and divalent cations. In liver fibrosis, A2M, combined with other serological proteins, is an indirect biomarker that correlates well with liver biopsy, particularly in advanced fibrosis. A2M quantification is integrated with other proteins in algorithms that generate a patient-specific score adjusted for age and sex to assess liver damage. The Diagam alpha-2-macroglobulin assay was evaluated on the Beckman Coulter DxC500AU. Analytical performance (precision, LoB, LoD, LoQ, linearity, and hook effect) was verified according to CLSI guidelines. Method comparison was performed using samples from La Pitié-Salpêtrière Hospital, the reference center for FibroTest in France. Analytical performance was evaluated according to CLSI guidelines: EP15-A3 for precision, EP17-A2 for LoB, and LoQ, and EP06-Ed2 for linearity. The hook effect was assessed by monitoring optical density as a function of antigen concentration. For method comparison (CLSI EP09c), at least 100 samples covering the pathophysiological range were measured on the DxC500AU and the cobas® 8000 (c502) at La Pitié-Salpêtrière Hospital, the reference center for FibroTest in France. Samples were also measured by nephelometry, a reference method for serum protein quantification because of its high accuracy and reliability. Results were analyzed using Passing–Bablok regression. Within run CV = 1.3 % at 1.21 g/L, 1.4 % at 2.42 g/L and 1.4 % at 3.17 g/L. Total CV = 1.7 % , 1.5 % and 1.5 % at the same concentrations, is agreement with the recommendation of the Vassault et al. (1). Method comparison: 124 fresh random samples distributed between 0.98 to 3.52 g/L, the Passing-Bablok regression presented a slope of 0.9442, an intercept of 0.0648 and R of 0.997 for cobas® 8000 (c502) VS DxC500; and a slope of 1.008, an intercept of 0.00335 and R of 0.989 for comparison with nephelometry. Estimated concentrations at 1, 2, and 4 g/L derived from the regression equations showed that the Diagam A2M assay provides results comparable to those obtained in the FibroTest context at La Pitié-Salpêtrière Hospital and are also in good agreement with nephelometry. In conclusion, the Diagam A2M assay showed satisfactory analytical performance and excellent agreement with routine methods and nephelometry, supporting its reliability for A2M measurement in the FibroTest context. (1) Analyses de biologie médicale: spécifications et normes d’acceptabilité à l’usage de la validation de techniques. A. Vassault et al. Ann Biol Clin 1999, 57 : 685-95.