Clinical enzymology

The diagnostic accuracy of three recommended methods for serum aspartate aminotransferase assays in patients suspected of myocardial infarction and hepatobiliary diseases

Serum aspartate aminotransferase (AST) activity was measured by the methods recommended by the Scandinavian Committee on Enzymes (SCE) and by the International Federation of Clinical Chemistry (IFCC) with pyridoxal phosphate (PLP) and without (-PLP) in one laboratory at 37 degrees C with the Abbott ABA-100 and in another at 30 degrees C with the IL Multistat III. Reference ranges were determined on 195 healthy hospital staff. Sera from 102 patients with suspected hepatobiliary disease (HBD) and 104 with suspected myocardial infarction (MI) were assayed at both laboratories by all three methods. Based on the above reference ranges, all assays with each method at both hospitals were abnormal in 59 of 67 cases with HBD and 53 of 55 with MI. In aggregate, all three methods yielded comparable rates of misclassification (20-23). The SCE method gave highest false negatives (18) and lowest false positives (5); the IFCC method gave lowest false negatives (1) and highest false positives (20); intermediate values of 8 false positives and 12 false negatives were given by the IFCC (-PLP) method. Using receiver operating characteristic (ROC) curves, the SCE method was clearly superior at 30 degrees C, and the IFCC (-PLP) method was marginally superior at 37 degrees C. However, when the decision threshold corresponded with a 2.5% false positive rate in the non-HBD, non-MI patients, the SCE method gave the lowest false negatives at both temperatures and, on the basis of the present data, must be considered to be the method of choice for AST activity determinations.

A kinetic method for quantification of aspartate aminotransferase isoenzymes

A spectrophotometric assay is proposed to determine the levels of aspartate aminotransferase (AAT) isoenzymes from chicken liver by a steady-state kinetic method which depends on the differential inhibition of these isoenzyme forms by high concentrations of substrate 2-oxoglutarate at pH 6.2. The use of a standard curve permits the determination of the percentage of chicken liver c-AAT and m-AAT isoenzymes. This method yields results in good correlation with those achieved by different extent adipate inhibition and by differential centrifugation.

Measurement of aminotransferases: Part 1. Aspartate aminotransferase

Aminotransferases are ubiquitous enzymes of mammalian cells and several are of important diagnostic use. The application of aspartate aminotransferase activity measurements in serum from individuals suffering from myocardial infarction brought about a new dimension in clinical laboratory testing in the 1950s. This review focuses on measurement techniques for aspartate aminotransferase and their application (a subsequent article will review other aminotransferases). Assay techniques measuring enzyme activity are direct spectrophotometric measurements, manometric techniques, assays using dye substances, coupled enzyme techniques, and radiometric procedures. Of these procedures, the one employing malate dehydrogenase and NADH is the most important and is covered in particular detail. The estimation of the mitochondrial isoenzyme of aspartate aminotransferase is also of clinical interest, in particular for estimating severity of disease or in specific applications (e.g., chronic alcoholism). Methods reviewed for estimation of this enzyme are electrophoresis, chromatography, differential kinetic behavior, and immunochemical separation. Determination of the enzyme protein by techniques independent of its catalytic activity are also reviewed.