Chemistry / Electrolytes
Creatine kinaseCK
Skeletal/cardiac/brain enzyme; the workhorse marker of muscle injury.
Sample
Serum
Clinical reference range
55 to 170 U/L
Adult male · Females ~30–135; Black race upper limit higher.
Conv: 55–170 U/L
Biology
What it measures
Catalyzes phosphocreatine ↔ ATP. Three isoenzymes: CK-MM (skeletal), CK-MB (cardiac), CK-BB (brain).
Clinical use
Why we order it
Rhabdomyolysis (>5× ULN), statin myopathy, inflammatory myopathies, MI (largely supplanted by hs-cTn).
Differential
Causes of abnormal values
Causes of HIGH
- ↑Rhabdomyolysis
- ↑Vigorous exercise (24–48 h post)
- ↑Statin myopathy
- ↑Polymyositis / dermatomyositis
- ↑Hypothyroidism
- ↑Trauma / IM injection
- ↑Seizure
Pitfalls
Pre-analytic & interpretation traps
- !Black patients and muscular individuals have higher baselines.
- !Rhabdomyolysis risk of AKI rises sharply when CK > 5,000 U/L.
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