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Serum Creatinine Phosphokinase (CPK) Activity

Published: August 9, 2026Updated: August 16, 2026

This test measures the activity of creatine phosphokinase (CPK), an enzyme found in heart, skeletal, and smooth muscle tissues. It helps assess muscle damage or injury.

Quick summary

["CPK levels can signal muscle injury or heart-related issues."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
79160-8
Short code
Cold agg pnl Ser
Synonyms
Cold agg pnl Ser
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What CPK Measures

CPK is an enzyme that plays a role in energy production within cells. When muscle or heart tissue is damaged, CPK leaks into the bloodstream, raising its levels. This test helps doctors identify sources of muscle injury, such as from exercise, trauma, or conditions like myositis or heart attacks.

Why It’s Done

Your healthcare provider may order a CPK test if you have symptoms like muscle pain, weakness, or fatigue. It’s also used to monitor conditions affecting muscles or the heart, such as myocarditis or rhabdomyolysis.

Common Causes of Elevated CPK

High CPK levels can result from muscle injuries (e.g., from exercise, strains, or trauma), certain medications, or underlying conditions like muscle disorders or heart problems. Low levels are less common but may occur with severe muscle wasting or certain genetic disorders.

When to Expect Results

Results may be available within 24 to 48 hours, depending on lab processing times. Follow-up with your provider to discuss findings and next steps.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

CPK (Serum)

Frequently asked questions

How soon after muscle injury will CPK levels rise?
CPK levels typically rise within 6 to 24 hours after muscle damage and peak around 24 to 48 hours. They return to normal within days to weeks, depending on the severity of injury.
Can CPK levels be affected by diet or supplements?
Dietary factors like protein intake or supplements (e.g., creatine) may influence muscle enzyme levels, but CPK specifically is less affected. Always discuss supplements with your provider.
Is CPK the same as CK-MB, which is often tested for heart issues?
No, CPK measures total enzyme activity, while CK-MB is a specific subtype linked to heart muscle damage. CK-MB is often tested separately for heart-related concerns.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy