Abstract
In order to reduce inter-assay variations in the measurement of the activities of lactate dehydrogenase (LD) in sera, we developed a technique to only measure isoenzyme LD1 in sample specimens using purified LD1 as an enzyme reference. We selected the rat LD1 isoenzyme as a reference enzyme after examing various thermostable enzymes, including those from tissue extracts of B. stearothermophilus, rat heart muscle, and human erythrocytes, and comparing their enzymic properties with human serum LD1. After measuring LD1 activities in 5 serum samples and 3 control sera using several commercially available LD assay systems as standards, we compared the coefficient of variation among the measured activity values. When we used LD assay systems with lactate as a substrate, we found that the inter-assay CV for the measurement of total LD and LD1 activities of these sera were 0.8-2.0% and 0.2-3.6%, respectivety. When we used pyruvate as the substrate, the CV were 5.3-7.8% and 0.7-6.3%, respectively. The interassay CV for the measurement of LD1 activities in sera were significantly smaller than that for the total LD activitiesin sera.
