Creatine kinase isoforms - plasma or serum

Last updated: Tuesday, 23, March, 2004

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Item Process

5 mL blood in lithium heparin or plain tube.



Reference Interval

CKMB2  0-1 U/L; CKMB2/CKMB1 ratio: 0-1.5.


For the diagnosis of myocardial infarction this test has been superseded by cardiac troponin T or I.


There are 3 isoforms of CKMM and 2 isoforms of CKMB in plasma. The CKMM3 isoform and the CKMB isoform are present intracellularly and released following myocardial infarction, but they are converted to CKMM1 and CKMB1 isoforms (respectively) after a few hours in plasma. Thus elevation of CKMM3/CKMM1 or CKMB2/CKMB1 ratios indicates recent release of CK and can be used as early, but non-specific, indicators of myocardial infarction.


Puleo PR et al. N Engl J Med 1994; 331: 561-566.