Creatine Kinase and Isoenzymes

Creatine Kinase and Isoenzymes

Synonym/acronym: CK and isoenzymes.

Common use

To monitor myocardial infarction and some disorders of the musculoskeletal system such as Duchenne’s muscular dystrophy.


Serum (1 mL) collected in a red- or red/gray-top tube. Serial specimens are highly recommended. Care must be taken to use the same type of collection container if serial measurements are to be taken.

Normal findings

(Method: Enzymatic for CK, electrophoresis for isoenzymes; enzyme immunoassay techniques are in common use for CK-MB)
Conventional & SI Units
Total CK
 Newborn–1 yrUp to 2 × adult values
 Male (children and adults)50–204 units/L
 Female (children and adults)36–160 units/L
CK Isoenzymes by Electrophoresis
CK-MB by Immunoassay0–3 ng/mL
CK-MB Index0–2.5
CK = creatine kinase; CK-BB = CK isoenzyme in brain; CK-MB = CK isoenzyme in heart; CK-MM = CK isoenzyme in skeletal muscle.The CK-MB index is the CK-MB (by immunoassay) divided by the total CK and then multiplied by 100. For example, a CK-MB by immunoassay of 25 ng/mL with a total CK of 250 units/L would have a CK-MB index of 10.Elevations in total CK occur after exercise. Values in older adults may decline slightly related to loss of muscle mass.


Creatine kinase (CK) is an enzyme that exists almost exclusively in skeletal muscle, heart muscle, and, in smaller amounts, in the brain and lungs. This enzyme is important for intracellular storage and release of energy. Three isoenzymes, based on primary location, have been identified by electrophoresis: brain and lungs CK-BB, cardiac CK-MB, and skeletal muscle CK-MM. When injury to these tissues occurs, the enzymes are released into the bloodstream. Levels increase and decrease in a predictable time frame. Measuring the serum levels can help determine the extent and timing of the damage. Noting the presence of the specific isoenzyme helps determine the location of the tissue damage. Atypical forms of CK can be identified. Macro-CK, an immunoglobulin complex of normal CK isoenzymes, has no clinical significance. Mitochondrial-CK is sometimes identified in the sera of seriously ill patients, especially those with metastatic carcinoma.

Acute myocardial infarction (MI) releases CK into the serum within the first 48 hr; values return to normal in about 3 days. The isoenzyme CK-MB appears in the first 4 to 6 hr, peaks in 24 hr, and usually returns to normal in 72 hr. Recurrent elevation of CK suggests reinfarction or extension of ischemic damage. Significant elevations of CK are expected in early phases of muscular dystrophy, even before the clinical signs and symptoms appear. CK elevation diminishes as the disease progresses and muscle mass decreases. Differences in total CK with age and gender relate to the fact that the predominant isoenzyme is muscular in origin. Body builders have higher values, whereas older individuals have lower values because of deterioration of muscle mass.

Serial use of the mass assay for CK-MB with serial cardiac troponin I, myoglobin, and serial electrocardiograms in the assessment of MI has largely replaced the use of CK isoenzyme assay by electrophoresis. CK-MB mass assays are more sensitive and rapid than electrophoresis. Studies have demonstrated a high positive predictive value for acute MI when the CK-MB (by immunoassay) is greater than 10 ng/mL with a relative CK-MB index greater than 3.

Timing for Appearance and Resolution of Serum/Plasma Cardiac Markers in Acute MI

Cardiac MarkerAppearance (hr)Peak (hr)Resolution (days)
CK (total)4–6242–3
Troponin I2–615–205–7

This procedure is contraindicated for



  • Assist in the diagnosis of acute MI and evaluate cardiac ischemia (CK-MB)
  • Detect musculoskeletal disorders that do not have a neurological basis, such as dermatomyositis or Duchenne’s muscular dystrophy (CK-MM)
  • Determine the success of coronary artery reperfusion after streptokinase infusion or percutaneous transluminal angioplasty, as evidenced by a decrease in CK-MB

Potential diagnosis

Increased in

  • CK is released from any damaged cell in which it is stored, so conditions that affect the brain, heart, or skeletal muscle and cause cellular destruction demonstrate elevated CK levels and correlating isoenzyme source CK-BB, CK-MB, CK-MM.

  • Alcoholism (CK-MM)
  • Brain infarction (extensive) (CK-BB)
  • Congestive heart failure (CK-MB)
  • Delirium tremens (CK-MM)
  • Dermatomyositis (CK-MM)
  • Head injury (CK-BB)
  • Hypothyroidism (CK-MM related to metabolic effect on and damage to skeletal muscle tissue)
  • Hypoxic shock (CK-MM related to muscle damage from lack of oxygen)
  • Gastrointestinal (GI) tract infarction (CK-MM)
  • Loss of blood supply to any muscle (CK-MM)
  • Malignant hyperthermia (CK-MM related to skeletal muscle injury)
  • MI (CK-MB)
  • Muscular dystrophies (CK-MM)
  • Myocarditis (CK-MB)
  • Neoplasms of the prostate, bladder, and GI tract (CK-MM)
  • Polymyositis (CK-MM)
  • Pregnancy; during labor (CK-MM)
  • Prolonged hypothermia (CK-MM)
  • Pulmonary edema (CK-MM)
  • Pulmonary embolism (CK-MM)
  • Reye’s syndrome (CK-BB)
  • Rhabdomyolysis (CK-MM)
  • Surgery (CK-MM)
  • Tachycardia (CK-MB)
  • Tetanus (CK-MM related to muscle injury from injection)
  • Trauma (CK-MM)

Decreased in

    Small stature (related to lower muscle mass than average stature) Sedentary lifestyle (related to decreased muscle mass)

Critical findings


Interfering factors

  • Drugs that may increase total CK levels include any intramuscularly injected preparations because of tissue trauma caused by injection.
  • Drugs that may decrease total CK levels include dantrolene and statins.

Nursing Implications and Procedure

Potential nursing problems

ProblemSigns & SymptomsInterventions
Coping (Related to a feeling of threat; inadequate support system; inadequate problem-solving ability; disease process; poor self-confidence)Inability to cope with the situation; inability to make decisions; inability to ask for help; fatigue; sleep disturbance; lack of confidence; inappropriate self-defense strategiesAssess for specific stressors that alter coping; identify the patient’s perception of stressors; assess for use of positive coping mechanisms; provide opportunities to express fear and anxiety in a safe, nonjudgmental environment; avoid false reassurance; convey acceptance and understanding; encourage patient to identify his or her own strengths; assist the patient to accurately evaluate current situation; reduce environmental stimuli that could be misunderstood as threatening; provide a safe outlet for personal feelings; use relaxation techniques; administer prescribed medication
Sleep (Related to perceived wellness and diagnosis; fear; anxiety; inadequate coping; medication side effect)Report of lack of sleep or rest; fatigue; decreased energy; restlessness; decreased level of concentration; irritability; listlessness; lethargy; malaise; daytime drowsiness; confusionAvoid loud noises; decrease lighting to a preferred restful level; administer prescribed medication; minimize interruptions; provide single-patient room if possible, if not possible a compatible roommate; assist the patient to identify the cause of his or her fear that results in insomnia; facilitate as much as possible the patient’s normal bedtime routine; limit daytime sleeping; collaborate with physician to revise medications that may be causing sleeplessness
Cardiac output (Related to prolonged myocardial ischemia; acute myocardial infarction; reduced cardiac muscle contractility; rupture papillary muscle; mitral insufficiency)Weak peripheral pulses; slow capillary refill; decreased urinary output; cool, clammy skin; tachypnea; dyspnea; altered level of consciousness; abnormal heart sounds; fatigue; hypoxia; loud holosystolic murmur; EKG changes; increased Jugular Venous Distention (JVD)Assess peripheral pulses and capillary refill; monitor blood pressure and check for orthostatic changes; assess respiratory rate, breath sounds, and orthopnea; assess skin color and temperature; assess level of consciousness; monitor urinary output; use pulse oximetry to monitor oxygenation; monitor EKG; administer ordered inotropic and peripheral vasodilator medications, nitrates; provide oxygen administration
Pain (Related to myocardial ischemia; myocardial infarction)Reports of chest pain; new onset of angina; shortness of breath; pallor; weakness; diaphoresis; palpitations; nausea; vomiting; epigastric pain or discomfort; increased blood pressure; increased heart rateAssess pain characteristics, squeezing pressure, location in substernal back, neck, or jaw; assess pain duration and onset (minimal exertion, sleep, or rest); identify pain modalities that have relieved pain in the past; monitor cardiac biomarkers (CK-MB, troponin, myoglobin); collaborate with ancillary departments to complete ordered echocardiography, exercise stress testing, pharmacological stress testing; administer prescribed pain medication; monitor and trend vital signs; administer prescribed oxygen; administer prescribed anticoagulants, antiplatelets, beta blockers, calcium channel blockers, angiotensin-converting enzyme (ACE) inhibitors, Angiotensin II receptor blockers (ARBs), thrombolytic agents


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in assessing for heart muscle cell damage.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s cardiovascular and musculoskeletal systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that a series of samples will be required. (Samples at time of admission and 2 to 4 hr, 6 to 8 hr, and 12 hr after admission are the minimal recommendations. Protocols may vary among facilities. Additional samples may be requested.) Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Nutritional Considerations: Increased CK levels may be associated with coronary artery disease (CAD). Nutritional therapy is recommended for the patient identified to be at risk for developing CAD or for individuals who have specific risk factors and/or existing medical conditions (e.g., elevated LDL cholesterol levels, other lipid disorders, insulin-dependent diabetes, insulin resistance, or metabolic syndrome). Other changeable risk factors warranting patient education include strategies to encourage patients, especially those who are overweight and with high blood pressure, to safely decrease sodium intake, achieve a normal weight, ensure regular participation in moderate aerobic physical activity three to four times per week, eliminate tobacco use, and adhere to a heart-healthy diet. If triglycerides also are elevated, the patient should be advised to eliminate or reduce alcohol. The 2013 Guideline on Lifestyle Management to Reduce Cardiovascular Risk published by the American College of Cardiology (ACC) and the American Heart Association (AHA) in conjunction with the National Heart, Lung, and Blood Institute (NHLBI) recommends a “Mediterranean”-style diet rather than a low-fat diet. The new guideline emphasizes inclusion of vegetables, whole grains, fruits, low-fat dairy, nuts, legumes, and nontropical vegetable oils (e.g., olive, canola, peanut, sunflower, flaxseed) along with fish and lean poultry. A similar dietary pattern known as the Dietary Approaches to Stop Hypertension (DASH) diet makes additional recommendations for the reduction of dietary sodium. Both dietary styles emphasize a reduction in consumption of red meats, which are high in saturated fats and cholesterol, and other foods containing sugar, saturated fats, trans fats, and sodium.
  • Social and Cultural Considerations: Numerous studies point to the prevalence of excess body weight in American children and adolescents. Experts estimate that obesity is present in 25% of the population ages 6 to 11 yr. The medical, social, and emotional consequences of excess body weight are significant. Special attention should be given to instructing the child and caregiver regarding health risks and weight-control education.
  • Recognize anxiety related to test results, and be supportive of fear of shortened life expectancy.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
  • Patient Education

    • Discuss the implications of abnormal test results on the patient’s lifestyle.
    • Provide teaching and information regarding the clinical implications of the test results, as appropriate.
    • Educate the patient regarding access to counseling services.
    • Provide contact information, if desired, for the AHA ( or the NHLBI (
    • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP.
    • Answer any questions or address any concerns voiced by the patient or family.
    • Teach the patient and family the importance of adequate rest in relation to their overall health.
    • Discuss with the patient and family factors that can interfere with adequate rest such as fear or anxiety.
  • Expected Patient Outcomes

    • Knowledge
    • Acquires understanding that irritability and mood changes are common with sleep deprivation
    • Recognizes that there are safe medications available that can be used to enhance sleep
    • Skills
    • Identifies measures that will increase the ability to obtain sleep or rest
    • Identifies nighttime foods or drinks that interfere with sleep
    • Attitude
    • Complies with the recommendation to limit daytime sleeping in order to enhance nighttime rest
    • Complies with the recommendation to take prescribed medication to enhance sleep if necessary

Related Monographs

  • Related tests include antiarrhythmic drugs, apolipoprotein A and B, AST, ANP, blood gases, BNP, calcium (blood and ionized), cholesterol (total, HDL and LDL), CRP, CT cardiac scoring, echocardiography, glucose, glycated hemoglobin, Holter monitor, homocysteine, ketones, LDH and isoenzymes, lipoprotein electrophoresis, magnesium, MRI chest, MRI venography, MI scan, myocardial perfusion scan, myoglobin, pericardial fluid, PET heart, potassium, triglycerides, and troponin.
  • Refer to the Cardiovascular and Musculoskeletal systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners