Early diagnosis of acute myocardial infarction by an immunoinhibition method for analysis of creatine kinase isoforms

: Conventional isoenzyme and enzyme values in serum usually are normal during the first few hours of acute myocardial infarction (AMI). Thus definitive diagnosis may be delayed. Measurement of serum creatine kinase (CK) isoform has begun to attract attention. In this study, we measured CK isoform with an immunoinhibition method in the first available samples from patients with AMI and from healthy subjects. In the 394 healthy subjects, the mean ratio of MM3 to MM1 of CK isoform was 0.494 +/- 0.1495 (SD). The upper limit of the reference values for this ratio was considered to be 0.793 (mean + 2 SD). In 40 of 48 patients, this ratio in the first available samples from patients with AMI was greater than 0.793. In 15 of 20 patients whose total CK activity was less than 260 IU/l, this ratio was greater than 0.793, while CK-MB activity measured with the immunoinhibition method was well within the reference range in all of these patients. Our results show that in the first available samples from patients with AMI, measurement of the ratio of MM3 to MM1 of CK isoform has the highest diagnostic efficiency. Thus, measurement of CK isoform with the immunoinhibition method can be applied for early diagnosis of AMI.