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Serum Creatinine Phosphokinase (CPK) Isoenzyme Activity (Total or Specific Subtype)

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

This test measures the activity of Creatine Phosphokinase (CPK), an enzyme found in heart, skeletal muscle, and brain cells. Elevated levels may indicate muscle damage or certain heart conditions.

Quick summary

["CPK helps identify muscle or heart tissue injury by detecting enzyme release into the bloodstream."]

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

Key facts at a glance

LOINC
79993-2
Short code
LV EF A4C MOD
Synonyms
LV EF A4C MOD
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-d-a-c-calc-by-single-plane-method-of-disks
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 Is Creatine Phosphokinase (CPK)?

CPK is an enzyme naturally present in heart, skeletal muscle, and brain tissues. When these tissues are damaged—such as from a heart attack, muscle strain, or injury—the enzyme leaks into the bloodstream, increasing its levels. This test measures CPK activity to assess potential damage.

Why Might You Need This Test?

Doctors may order CPK testing to evaluate symptoms like muscle weakness, chest pain, or unexplained fatigue. It’s also used to monitor conditions like heart disease, muscle disorders, or after trauma or surgery.

When Might Results Be Abnormal?

Elevated CPK levels often signal recent muscle injury (e.g., exercise, injury) or heart issues (e.g., heart attack). Very high levels may require further investigation to rule out conditions like myositis or rhabdomyolysis.

What Does It Mean If Results Are Low?

Low CPK levels are less common but may occur in certain genetic disorders or severe muscle wasting. They’re rarely a standalone concern unless combined with other symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

CPK Total Activity

Frequently asked questions

How is CPK Tested?
A blood sample is drawn, and CPK activity is measured using an enzymatic method. Results are reported in units per liter (U/L) or milliliters (U/mL), depending on the lab’s standard.
What Can Affect CPK Levels?
Factors like strenuous exercise, muscle trauma, infections, or certain medications (e.g., statins) can temporarily raise CPK. Hormonal imbalances or genetic conditions may also influence baseline levels.
How Long Does It Take to Get Results?
Results are typically available within 24–48 hours, depending on lab processing times. Follow-up may require additional testing if initial results are concerning.
  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