Creatine Kinase and Isoenzymes

General

Synonym/Acronym:
CK and isoenzymes.

Rationale
To monitor MI and some disorders of the musculoskeletal system, such as Duchenne muscular dystrophy. The use of CK for monitoring MI and disorders of the musculoskeletal system has largely replaced myoglobin.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
Method: Enzymatic for CK, electrophoresis for isoenzymes; enzyme immunoassay techniques are in common use for CK-MB.

Conventional and SI Units
Total CK
  Newborn–1 yrUp to 2 × adult values
  Male (children and adults)50–204 units/L
  Female (children and adults)36–160 units/L
CK Isoenzymes by Electrophoresis
  CK-BBAbsent
  CK-MB0–4%
  CK-MM96–100%
CK-MB by Immunoassay0–5 ng/mL
CK-MB Index0–2.5
CK = creatine kinase; CK-BB = CK isoenzyme in brain; CK-MB = CK isoenzyme in heart; CK‑MM = CK isoenzyme in skeletal muscle.The CK-MB index is the CK-MB (by immunoassay) divided by the total CK and then multiplied by 100. For example, a CK-MB by immunoassay of 25 ng/mL with a total CK of 250 units/L would have a CK-MB index of 10.Elevations in total CK occur after exercise. Values in older adults may decline slightly related to loss of muscle mass.

Critical Findings and Potential Interventions
N/A

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