Diagnostic efficiency of four lactate dehydrogenase isoenzyme-1 ratios in serum after myocardial infarction.

We compared the diagnostic efficacy of the ratios LD-1/LD-2, LD-1/LD-3, LD-1/LD-4, and LD-1/LD-5 in 69 documented cases of myocardial infarction. We used 149 patients with congestive heart failure and 67 patients with nonmyocardial infarct as controls. We used a computer program to produce receiver-operating characteristic curves, decision threshold plots, and likelihood ratios for these LD ratios at 6-h intervals up to 108 h after the onset of chest pain or hospital admission. All ratios in the myocardial infarction cases peaked around 36 h after the onset of chest pain, while those for the nonmyocardial and congestive cardiac failure cases did not change over the 108-h period. In all patients with infarctions, LD-1/LD-4 and LD-1/LD-5 increased by 1.7 times (when LD-1 was less than 40%) and 3.4 times (when LD-1 was greater than 40%), respectively, over control values. Optimum decision threshold values were obtained at 13-24 h (LD-1/LD-5), 31-36 h (LD-1/LD-4 and LD-1/LD-3), and 55-60 h (LD-1/LD-2) after onset of symptoms. The highest likelihood ratio was obtained with the LD-1/LD-4 ratio; therefore, we suggest that this is a better diagnostic test for myocardial infarction than LD-1/LD-2.