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What is a Creatine Phosphokinase (CPK) test?

A CPK test, also known as creatine kinase (CK) test, is a blood test that evaluates the amount of the enzyme CPK in the body. CPK is mainly found in the brain and cardiac as well as skeletal muscles. It helps in the proper functioning of our muscles. 

CPK is normally found in minute amounts in the bloodstream, though, its levels increase when there is some damage to the muscles or interference with muscle energy production. So, a CPK test is done to look for muscle damage in the body.

Some conditions that can result in muscular damage include strenuous exercise, inflammation (myositis), myopathies (such as muscular dystrophy) and rhabdomyolysis (a disease of extreme muscle breakdown and leads to extremely high levels of CPK)

  1. Why is a CPK test performed?
  2. How do you prepare for a CPK test?
  3. How is a CPK test performed?
  4. What do CPK test results indicate?

A CPK test is performed when muscle damage is expected or when a person shows apparent symptoms of a muscle injury, such as

  • Muscle aches or pain
  • Muscular weakness
  • Restricted muscle movements
  • Muscle spasms
  • Muscle soreness
  • Dark-coloured urine (urine turns darker due to the presence of myoglobin, a substance released by damaged muscles, which can affect kidneys)

This test is also performed at regular intervals for monitoring continual damage. Furthermore, it is useful for diagnosing myopathies, such as muscular dystrophy and trauma such as burns or crush injuries.

CPK has three isoenzymes present in different locations, which helps in determining the precise area of the damage:

  • CPK-MB (found in the heart muscle)
  • CPK-MM (found in the skeletal muscle)
  • CPK-BB (found in the brain)

No special preparations are needed for this test.

An experienced laboratory specialist will collect a blood sample from a vein in your arm by inserting a small needle. A small quantity of blood will be withdrawn into a sterile vial or a test tube, which will be capped properly and sent to a lab for analysis.

You may feel a momentary pricking pain when the needle goes into the vein. Apart from that, there is a minimal risk of pain, light-headedness and bruising at the site of injection. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the blood withdrawal site. Make sure to check in with your doctor if the symptoms persist.

CPK levels are expressed as micrograms per litre (mcg/L).

Normal results: Normal levels of CPK range from 10 to120 mcg/L.

Abnormal results: 

High levels of CPK are seen in case of:

A moderately high level of CPK is seen during or after strenuous exercises, after a prolonged workout session or after a sport session.

People having greater muscle mass are known to have high levels of CPK; thus, males have relatively higher levels over females. Any injury to muscles, such as taking an injection, can temporarily raise CPK levels. During early pregnancy, CPK levels tend to be on the lower side.

CPK was once used primarily to diagnose heart attacks, but it is now replaced by troponin level evaluation; however, it is still used to diagnose a heart attack that occurs immediately after the first one.

CPK is usually evaluated along with certain other tests, including electrolyte levels, blood urea nitrogen (BUN), creatinine levels and urine myoglobin levels (when rhabdomyolysis is suspected)

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. Richard A. McPherson, Matthew R. Pincus. Henry's Clinical Diagnosis and Management by Laboratory Methods E-Book. Elsevier Health Sciences, 2017. [internet].
  2. Anderson JL. Acute Myocardial Infarction. N Engl J Med. 2017 May 25;376(21):2053-2064. PMID: 28538121
  3. Eric J. Topol, Robert M. Califf. Textbook of Cardiovascular Medicine. Lippincott Williams & Wilkins, 2007
  4. Walker HK et.al .Clinical Methods: The History, Physical, and Laboratory Examinations.. Boston: Butterworths; 1990.ISBN-10: 0-409-90077-X
  5. The Muscular Dystrophy Association. Simply Stated: The Creatine Kinase Test. Chicago, USA.
  6. MedlinePlus Medical: US National Library of Medicine; Rhabdomyolysis
  7. Health Harvard Publishing. Harvard Medical School [Internet]. Muscle Strain. Harvard University, Cambridge, Massachusetts.