Immunochemical LD1 assay for myocardial infarction.

The diagnostic efficiency of an immunochemical assay for LD1 (I-LD1) was compared with an electrophoretic procedure for this isoenzyme (E-LD1) in 100 consecutive patients hospitalized for a clinical suspicion of acute myocardial infarction (MI). All patients were investigated with a standard protocol including serial determinations of total creatine kinase (CK) and lactic dehydrogenase (LD) activities, CK and LD isoenzymes, and electrocardiograms. Thirty-two patients were diagnosed to have acute MI on the bases of positive CK-MB or EKG or both. The coefficients of variation for the intraassay and interassay precision of I-LD1 assay ranged from 3.12% to 7.69%. Direct correlation between the I-LD1 and E-LD1 was very satisfactory (r = .961; P = less than .001). When the results of these two procedures were compared in terms of decision values for acute MI, there was agreement between them in 87 patients. At the cut-off point of 90 U/L, I-LD1 assay was 100% sensitive and 89% specific for acute MI; the corresponding figures for E-LD1 were 81% and 91%, respectively. The diagnostic efficiencies of the I-LD1 and E-LD1 procedures were 93% and 88%, respectively. A substantial saving in technologist time with the I-LD1 assay over the E-LD1 procedure was documented in this study.