Chemistry: The Lack of Diagnostic Utility of Lactate Dehydrogenase Isoenzymes: Evaluation of Acute Myocardial Infarction

This retrospective study evaluated 178 clinically diagnosed acute myocardial infarctions (AMIs) in which creatine kinase (CK-MB) and lactate dehydrogenase (LD) isoenzyme levels were studied. An LD “flip” (LD1/LD2 > 1.0) was not demonstrated in 69.1% of the events. Of the AMIs manifesting an LD flip, only 13% (7/55) were negative for CK-MB isoenzyme elevations, and 5 out of 7 of these had already been diagnosed as an AMI at another institution. The remaining two events were characterized by diagnostic clinical and electrocardiographic changes that alone would have sufficed for the diagnosis of AMI. We conclude that LD isoenzyme levels were of no clinical benefit in any AMI case studied.