Table of Contents
Definition / general | Terminology | Pathophysiology | Diagrams / tables | Interpretation | Laboratory | Additional referencesCite this page: Bernstein L. Creatine kinase. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/chemistrycardiacCK.html. Accessed December 24th, 2024.
Definition / general
- Muscle related enzyme released into blood after muscle cell death
- Serum levels are used to diagnosis acute myocardial infarction, rhabdomyolysis, muscular dystrophy and acute renal failure
Terminology
- Also known as CK, creatine phosphokinase (CPK), phospho-creative kinase, EC 2.7.3.2
- "Creatinine kinase" is an incorrect term
- Creatinine is a break-down product of creatine phosphate in muscle produced at a fairly constant rate, and used to calculate creatinine clearance and glomerular filtration rate
Pathophysiology
- Present in heart, brain, skeletal and intestinal smooth muscle (acts as energy reservoir for rapid rebuffering and regeneration of ATP), but in different concentrations and with different ratios of the M (muscle) and B (brain) dimeric units
- CK from brain almost never crosses the blood-brain barrier
- There are three different isoenzymes: CK-MM, CK-BB and CK-MB
- Skeletal muscle expresses CK-MM (98%) and low levels of CK-MB (1% in type 1 fibers, 2 - 6% in type 2 fibers, higher amounts during skeletal muscle regeneration)
- Myocardium expresses CK-MM (70%) and CK-MB (25 - 30%, higher in right heart than left heart)
- Creatine kinase catalyses the conversion of creatine to phosphocreatine, consuming adenosine triphosphate (ATP) and generating adenosine diphosphate (ADP)
Interpretation
Acute myocardial infarction
- Markers are ordered as a panel, because different markers have different time frames for detection
- American College of Cardiology / American Heart Association recommend results within 30 - 60 minutes of admission, which precludes prolonged serial measures of serum levels of markers
- Suggested point of care multimarker algorithm to detect acute MI:
- Troponin I >= 0.4 ng/mL (0.4 μg/L) in any specimen
- Doubling of myoglobin between 2 sequential specimens with any detectable TnI at least by the second of the 2 specimens, or
- Myoglobin (doubling) and CK-MB concentrations increasing by 50% or more in 2 or 3 specimens (Am J Clin Pathol 2008;129:788)
- Algorithm for CK-MB testing:
- If total CK < 80 IU/L, don’t do CK-MB
- Do CK-MB (reference range is 0 - 4.9 ng/mL) if total CK is between 80 - 500 IU/L
- Do CK-MB (no reference range) and CK-MB% (reference range 0.0 - 1.0%) if total CK > 500 IU/L
Laboratory
Test methodology
CK-MB Mass Assay
Test indications
Test limitations
Reference ranges
- Continuous Spectrophotometric Rate Determination
- Temperature: 30 degrees C, pH: 7.4
- Wavelength: A340nm
- Light path: 1 cm
CK-MB Mass Assay
- An immunometric assay using a monoclonal antibody, in which CK-MB is considered an antigen
- Test can be reported in < 1 hour using various automatic platforms
- Qualitative level is usually reported with relative index / relative percent (CK-MB / total CK)
- Values suggestive of acute MI are 5 ng/ml or greater and relative index of 2% or greater (Abbott Point of Care: Creatine [Accessed 20 December 2021], BeckmanCoulter)
Test indications
- CK levels were historically used in emergency room patients to test for myocardial infarction (now often replaced by troponin), rhabdomyolysis, muscular dystrophy, myositis, myocarditis, malignant hyperthermia, neuroleptic malignant syndrome
- Levels are determined specifically in patients with chest pain and cardinal features of chest pain
- Activity is estimated in the course of acute ischemic heart disease to diagnose acute myocardial infarction (AMI) and to estimate infarct size
- CK-MB activity is normal in 25 - 50% of patients with MI at time of admission (Emerg Med Clin North Am 2001;19:321), rises some 4 - 6 hours after the onset of chest pain, peaks within 12 - 24 hours, and returns to baseline levels within 36 - 48 hours
- These times may be shorted considerably by thrombolytic therapy
Test limitations
- High serum levels indicate injury to muscle, including rhabdomyolysis, myocardial infarction, muscular dystrophy, myositis, myocarditis, malignant hyperthermia and neuroleptic malignant syndrome
- Also seen in hypothyroidism
- The use of statin medications, commonly used to decrease serum cholesterol levels, may be associated with elevation of the CPK level in 1% of the patients taking these medications, and with actual muscle damage in a much smaller proportion
- CK-MB and CK-BB are quite labile
- Specimens should be frozen if the assay cannot be performed within 24 hours
Reference ranges
- Normal values are usually between 25 and 200 U/L, may be lower in women
- High values for CK-MB: need to be interpreted in the context of chest pain and ECG findings or other muscle damages
- Patients whose CK does not decline 50% or more within 48 hours of peak have increased risk of reinfarction or death (Clin Chem 1989;35:414)
Additional references