Measuring all the isoforms of the CK enzyme can be done to assess myocardial necrosis. However, this test requires high-voltage isoelectric focusing (a type of electrophoresis). With this method, subtypes of CK-MM and CK-MB can be isolated. They are released in myocyte necrosis and are not ordinarily in peripheral circulation. CK-MB has 4 isoforms; CK-MB1 and CK-MB2 are released 2 – 4 hours after chest pain, peak in 6 – 9 hours, and like myoglobin, are early markers of an AMI.
CK-isoforms are very rarely ordered. Because their measurement takes a long time, electrophoresis is a slow technique, this testing has no role in evaluating AMI and acute cardiac syndromes.
When CK-isoforms are measured, most often a ratio of CK-MB2/CK-MB1 is reported. A ratio of <1 is negative for myocardial necrosis; a ratio >1.7 is positive for myocardial necrosis.
