Creatine kinase B-subunit activity in human serum. II. Evaluation of s-ck b-subunit activity in the diagnosis of acute myocardial infarction.

In a group of 113 consecutive patients taken into a coronary care unit on suspicion of acute myocardial infarction, blood samples were taken every 6 h and the following enzyme activities were measured: creatine kinase (S-CK), aspartate aminotransferase (S-ASAT), alanine aminotransferase (S-ALAT) and lactate dehydrogenase (S-LD). All measurements were made according to the Recommendations of the Scandinavian Committee on Enzymes. On all patients S-CK B subunit activity was determined by immunoinhibition with a specific anti CK M-subunit inhibitory antibody. At peak values of the respective total enzyme activities CK and LD isoenzymes were further qualitatively estimated by electrophoresis. The data indicate that even serial determinations of total CK, ASAT, ALAT and LD activities in serum do not provide the information required for a conclusive diagnosis of myocardial infarction in the individual case. In contrast, the positive predictive value (PV) of S-CK B was found to be 1.0 and the negative predictive value was 0.98. S-CK MB showed a PV pos. of 1.0 and also a PV neg. of 1.0. Electrophoretic determination of S-LD isoenzymes was slightly poorer with a PV pos. of 0.96 and PV neg. of 0.98. S-CK, total activity with nearly 9 per cent false positives had a positive predictive value of only 0.91, but a negative one of 1.0.