Creatine Kinase and Isoenzymes

Test Description:

Creatine kinase (CK) is an enzyme found primarily in the heart and skeletal muscles,
and in smaller amounts in the brain. When the total CK level is substantially elevated,
it usually indicates injury or stress to one or more of these areas. When a muscle is
damaged, CK leaks into the bloodstream. Determining which isoenzyme (specific
form of CK) is elevated will help determine which tissue has been damaged.
CK can be measured as the total enzyme in the serum, or each of its three
isoenzymes may be measured. The isoenzymes include:

CK1 (CPK-BB): produced primarily by brain tissue and smooth muscle of the lungs
CK2 (CPK-MB): produced primarily by heart tissue
CK3 (CPK-MM): produced primarily by skeletal muscle
CK, along with asparate aminotransferase (AST) and troponin, is assessed in the
case of suspected myocardial infarction. It typically appears in the bloodstream within
3 to 6 hours of the tissue injury, with peak values occurring 18 to 24 hours postinjury.
CK levels are usually elevated for approximately 2 to 3 days. Thus, CK is one of the
first cardiac enzymes to become elevated following a myocardial infarction.
Creatine kinase practice  evidence 

The Third Report of the Adult Treatment Panel III (ATP III) recommends that baseline
CK levels be checked upon initiating statin therapy, the rationale being that
asymptomatic CK elevations are relatively common. Determining the patient’s pretreatment
CK levels will prevent inappropriately attributing CK elevation to statin
therapy in the event of muscle complaints later and assuming the presence of
rhabdomyolysis.

Normal Values

Total CK
Female: 40–150 U/L (0.67–2.50 μkat/L SI units)
Male: 38–174 U/L (0.63–2.90 μkat/L SI units)

Isoenzymes

CK1 (CPK-BB): 0–1%
CK2 (CPK-MB): <3%
CK3 (CPK-MM): 95–100%

Possible Meanings of Abnormal Values

Increased Total CK                                 Decreased Total CK

Acute cerebrovascular disease                  Addison’s disease
Acute psychosis                                        Anterior pituitary hyposecretion
Alcoholism                                                Connective tissue disease
Brain trauma                                             Early pregnancy
Cardiac defibrillation                                Hepatic disease
Cardiac surgery                                         Low muscle mass
Convulsions                                               Metastatic neoplasia
Delirium tremens
Dermatomyositis
Electrical shock
Hypokalemia
Hypothyroidism
IM injections
Muscle inflammation
Myocardial infarction
Myxedema
Polymyositis
Progressive muscular dystrophy
Pulmonary infarction
Rhabdomyolysis

Increased CK1 (CPK-BB) Isoenzyme

Brain tissue injury
Brain tumors
Cancer of breast, lung, prostate
Cerebrovascular accident
Pulmonary infarction
Seizure
Shock

Increased CK2 (CPK-MB) Isoenzyme

Acute myocardial infarction
Cardiac defibrillation
Congestive heart failure
Electrical injuries
Malignant hyperthermia
Myocarditis
Reye’s syndrome
Trauma to heart

Increased CK3 (CPK-MM) Isoenzyme

Hypokalemia
Hypothyroidism
IM injections
Myocardial infarction
Muscle inflammation
Muscle necrosis
Muscular dystrophy
Myositis
Polymyositis
Postoperative period
Rhabdomyolysis
Shock
Strenuous exercise

Contributing Factors to Abnormal Values

• Hemolysis of the blood sample or strenuous exercise prior to the test will alter test results.
• Factors that may affect test results include cardiac catheterization, intramuscular
injections, trauma to muscles, recent surgery, and prolonged exercise.
• Drugs which may increase total CK: amphotericin B, ampicillin, anticoagulants,
aspirin, clofibrate, cocaine, dexamethasone, ethanol, furosemide, lithium, morphine,
and some anesthetics.

Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• Inform the patient that this test is often performed on three consecutive days, and again
in one week, necessitating multiple venipunctures.
• No fasting is required prior to the test.
• Do not administer any intramuscular injections for 1 hour prior to the test.

Procedure

• A 7-mL blood sample is drawn in a red-top collection tube.
• Gloves are worn throughout the procedure.

Posttest

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
  bleeding.
• Label the specimen and transport it to the laboratory.
• Report abnormal findings to the primary care provider.