Chemistry
Cardia related
Creatine Kinase isoenzyme MB (CKMB)

Author: Larry Bernstein, M.D. (see Authors page)

Revised: 2 February 2016, last major update March 2011

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Creatine Kinase isoenzyme MB [title]
Cite this page: Creatine kinase isoenzyme MB (CKMB). PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/chemistrycardiacCKMB.html. Accessed December 8th, 2016.
Definition / General
  • Sensitive and specific test for myocardial infarction, now widely replaced by troponin
Pathophysiology
  • Catalyzes the conversion of creatine to phosphocreatine, consuming adenosine triphosphate (ATP) and generating adenosine diphosphate (ADP)
Clinical Features
  • CK isoenzyme MB rises some 4 - 6 hours after the onset of chest pain, peaks within 12 - 24 hours, and returns to baseline levels within 24 - 48 hours
  • CK-MB is usually ordered, along with total CK in persons with chest pain to determine whether the pain is due to myocardial infarction
  • May also be ordered in a person with a high CK to determine whether damage is in the heart
Laboratory
Test methodology
  • Electrophoresis:
    • Serum creatine kinase (CK) is separated into 3 isoenzymes by electrophoretic separation on agarose gel
    • Colorimetric results allow for improved workflow management as the gels do not have to be scanned immediately
    • The permanent patterns combined with a clear gel background means scanning and quantitation are easy
  • Immunoassays are also commonly used

Test indications
  • Troponin has largely replaced CK-MB in many hospitals, although some centers still rely on CK-MB (Wikipedia - CPK-MB test)

Test limitations
  • Some patients have a variant of CK-BB called "Macro CK", which complexes to IgG or IgA antibody
    • It migrates between MM and BB on the gel, and may falsely increase CK-MB values
  • CK-MB can be elevated with massive rhabdomyolysis, even though the concentration is low in skeletal muscle
  • Electrophoresis of CK with values of total CK under 100 U/L may cause false positive CK-MB values

Reference ranges
  • If the value of CK-MB is elevated and the ratio of CK–MB to total CK (relative index) is more than 2.5 - 3, it is likely that the heart was damaged
  • A high CK with a relative index below 2.5 - 3.0 suggests that skeletal muscle and not cardiac muscle was damaged