Chemistry, toxicology & urinalysis
Organ specific
Cardiac
CK-MB (creatine kinase isoenzyme MB)


Topic Completed: 1 March 2011

Minor changes: 27 June 2020

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: Creatine Kinase isoenzyme MB [title]

Larry Bernstein, M.D.
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Cite this page: Bernstein L. CK-MB (creatine kinase isoenzyme MB). PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/chemistrycardiacCKMB.html. Accessed April 13th, 2021.
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
Board review style question #1

    This is an image of a creatinine kinase electrophoresis. This is an image of a creatinine kinase electrophoresis:

  1. 32 year old healthy male who just finished a marathon
  2. 45 year old female with widely metastatic breast cancer
  3. 55 year old male with acute onset chest pain
  4. 78 year old asymptomatic female
Board review style answer #1
D. A 78 year old asymptomatic female - this is the CK electrophoretic pattern seen in macro CK, a benign finding in healthy, elderly females. Macro CK is a result of a CK antibody conjugate and typically appears between CK-MM and CK-MB.

Choices 'a' and 'b' would not have a macro CK band. A 45 year old female (c) may have an additional band that migrates to the right of CK-MM. This band is mitochondrial CK and is seen in patients with widely metastatic disease.
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