Development of a Rapid Microparticle-enhanced Turbidimetric Immunoassay for Plasma Fatty Acid-binding Protein, an Early Marker of Acute Myocardial Infarction

Abstract

Heart-type fatty acid-binding protein (FABP; M r 14 500) is an early plasma marker of acute myocardial infarction (AMI) (1)(2)(3). FABP shows increased plasma concentrations within 3 h after AMI and returns to a normal reference interval within 12–24 h, thereby resembling myoglobin (4)(5). However, the diagnostic specificity and sensitivity of FABP for AMI detection are better than those of myoglobin (6)(7). FABP is also found in skeletal muscle, but the determination of the plasma ratio of myoglobin over FABP allows the discrimination between myocardial and skeletal muscle injury (4)(5). The application of FABP as an early plasma marker in routine clinical practice requires the availability of a rapid assay system. Several immunochemical assays for FABP have been described, taking an assay time of 2–16 h (2)(3)(8)(9). Recently, a one-step ELISA for plasma FABP with a total performance time of 45 min (10) and an amperometric enzyme immunosensor assay taking 27 min per plasma sample were described (11). However, these assays are of limited use for routine clinical practice. We describe here a microparticle-enhanced turbidimetric immunoassay for FABP that offers the advantages of being precise, easy to perform, rapid, and fully automated. Latex reagent was prepared by physical adsorption onto carboxylated latex particles of three monoclonal anti-human FABP antibodies that recognize distinct epitopes (12), which were then stored in 10 mmol/L Tris-HCL, pH 8.0, containing 5 g/L bovine serum albumin, 0.01 g/L Tween 20, 1 g/L NaN3, and 50 g/L sucrose. The assay was performed by using a COBAS® MIRA Plus analyzer (F. Hoffmann-La Roche Ltd.). Briefly, 75 μL of latex reagent was mixed with 155 μL of reaction buffer (22 mmol/L phosphate buffer, pH 7.0, 350 mmol/L NaCl, 2 …