Immunochemical determination of LDH-1

An evaluation of a new immunochemical method for the heart isoenzyme of lactic dehydrogenase (LDH-1) is described. In this assay, a goat antibody against the M subunit of LDH is added to a patient's serum. Donkey antigoat gamma globulin is then added, which precipitates the M-anti-M complex. LDH activity in the supernatant is thus a measure of the heart isoenzyme, since this isoenzyme is not precipitable by the anti-M antibody. Assays for total CK, CK-MB, and total LDH, and LDH electrophoresis were performed along with an immunochemical LDH-1 assay on 261 serum samples from 49 patients clinically suspected to have acute myocardial infarctions. These were performed on admission and 12, 24, 48, 72, and 96 hours later. The diagnosis of acute infarction was confirmed for 25 of the 49 patients and ruled out for 19. Five patients were classified clinically as borderline cases for the diagnosis of acute myocardial infarction. All 25 patients with the clinical diagnosis of myocardial infarction had positive results by both electrophoresis and immunochemistry; four of the five borderline patients had positive results by electrophoresis. All five borderline patients had positive results by immunochemistry. None of the 19 patients without apparent myocardial injury had positive results by either electrophoresis or immunochemistry. Ten (40%) of the 25 samples collected at the time of admission from 25 patients who had myocardial infarctions had elevated LDH-1 activity by electrophoresis, while 14 patients (56%) had increased LDH-1 by immunochemistry. The immunochemical method for LDH-1 is more sensitive than electrophoresis for the detection of myocardial infarction and offers the further advantages of greater simplicity, precision, and accuracy, while being no less specific.