Sources of error in spectrophotometric measurement of aspartate aminotransferase and alanine aminotransferase activities in serum

Abstract

The authors examined the measurement of serum aspartate and alanine aminotransferase activities with a short interval enzyme activity analyzer. Double beam spectrophotometry was used to elucidate the source of errors in such measurements. For both enzymes the principal error sources are the presence of endogenous substrate for lactate dehydrogenase, and the reaction of 2 oxoglutarate with serum glutamate dehydrogenase and ammonium ions added to the reaction mixture in admixture with the secondary enzymes of the coupled reactions. In the case of serum aspartate aminotransferase, a less important source of error is the reaction of serum alanine aminotransferase with endogenous substrate. Use of 2 oxoglutarate as a reaction initiator in conventional methods causes errors. Suitable blank reagent mixtures are described that permit accurate, rapid measurement of these activities by double beam spectrophotometry in a short interval enzyme activity analyzer.