Quantitation of cumulative release of lactate dehydrogenase isoenzyme-1 in plasma of patients with acute myocardial infarction using a commercially available test

In 27 patients with acute myocardial infarction (AMI) we calculated cumulative release of alpha-hydroxybutyrate dehydrogenase (alpha HBDH) per liter plasma which is a routine procedure in our coronary care unit, and compared these values with calculated cumulative release of lactate dehydrogenase isoenzyme-1 (LDH-1) per liter plasma using a LDH-1 test that has become commercially available recently. Theoretically, myocardial (iso)enzyme release is more accurately determined with LDH-1 than with alpha HBDH, due to the higher cardiac specificity of LDH-1 compared to alpha HBDH. The only disadvantage of LDH-1 is its abundance in erythrocytes necessitating a correction by measurement of free hemoglobin (Hb) concentration in plasma. After division of cumulatively released activities (Q72) of alpha HBDH and LDH-1 by the activities per gram of normal myocardium (135 and 81 U/g, respectively), the values of Q72(alpha HBDH)/135 and Q72(LDH-1)/81 were compared per patient. Elevated alpha HBDH levels in the presence of normal creatine kinase levels in plasma samples taken on admission, as well as hemolysis gave rise to overestimation of cumulative release of alpha HBDH as compared to LDH-1, but hepatic congestion occurring secondary to AMI (48-72 h after onset of infarction) did not disturb the equality of Q72 (alpha HBDH)/135 and Q72(LDH-1)/81 values. In 16 patients showing none of the mentioned conditions, the relation between Q72(alpha HBDH)/135 and Q72(LDH-1)/81 coincided with the line of identity (r = 0.97). We conclude that the use of an easy and rapid plasma LDH-1 assay improves the assessment of enzymatic infarct size, provided free Hb levels are measured to correct LDH-1 activities for a contribution by erythrocytes.