When Is Creatine Kinase and CKMB considered significant in Acute Myocardial Infarction?

I read two interesting articles that mentioned about the biochemical markers in AMI.Question 1: When Is Creatine Kinase and CKMB considered significant in Acute Myocardial Infarction?Creatinine Kinase (CK) and Creatine Kinas-MB (CK-MB) is significant when [in the presence of other supportive criteria like typical chest pain, etc] 1. CK elevated ≥ 2x upper laboratory normal and/or2. CK-MB