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

Topic Completed: 1 March 2011

Minor changes: 27 June 2020

Copyright: 2002-2020,, Inc.

PubMed Search: Creatine Kinase isoenzyme MB [title]

Larry Bernstein, M.D.
Page views in 2019: 2,880
Page views in 2020 to date: 1,537
Cite this page: Bernstein L. CK-MB (creatine kinase isoenzyme MB). website. Accessed September 29th, 2020.
Definition / general
  • Sensitive and specific test for myocardial infarction, now widely replaced by troponin
  • 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
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 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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