Measuring all the isoforms of the CK enzyme can also 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, CK isoforms, 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.