Creatine kinase (CK, also known as creatine phosphokinase (CPK) or phospho-creatine kinase) is an enzyme mainly expressed by the muscles and the heart muscle.
CK catalyzes the reversible phosphorylation reaction:
ADP + creatine phosphate → ATP + creatine
This reaction generates ATP 9adenosine triphosphate) from PCr (phosphocreatine) and ADP (adenosine diphosphate).
When a muscle is damaged the level of CK is elevated. Therefore the CK test may be used to detect the injury to CK-reach tissue which are skeletal muscles and myocardium (the heart muscle).
CK is a dimeric molecule, composed of M and B subunits. The 2 subunits can form 3 isozymes: CK-MM mainly found in the skeletal muscles; CK-MB found in myocardium; and CK-BB found in neuronal tissue. The normal value for CK-MB is 3-5% of total CK, but peak CK-MB level can range from 15-30% of total CK in post-myocardial infarction. However, a CK-MB fraction more than 6% of the total CK activity is regarded as diagnostic for myocardial infarction.
The level of CK are:
6-11 years: 150-499 U/L
12-17 years: 94-499 U/L
> or =18 years: 52-336 U/L
6-7 years: 134-391 U/L
8-14 years: 91-391 U/L
15-17 years: 53-269 U/L
> or =18 years: 38-176 U/L
Check out the Creatinekinase Test
The test may be ordered when a person presents symptoms of muscle injury such as:
– Muscle pain or aches;
– Muscle weakness;
– Dark urine (this may be caused by the presence of myoglobin, a substance released by damaged muscles);
– Historically CK-MB was measured in case of myocardial infarction, although now this test is still sometimes performed to detect a new infarction soon after the first one.
Increased CK is predominantly used to diagnose neuromuscular diseases and acute myocardial infarction.
Total CK is increased in case of:
– myopathies and muscular dystrophies (Duchenne’s);
– muscular dystrophy;
– rhabdomyolysis – a condition in which damaged skeletal muscle breaks down rapidly.;
– drug-induced myopathies;
– neuroleptic malignant syndrome;
– malignant hyperthermia;
– periodic paralyses;
– cardiac damage (due to myocardial infarction, myocarditis, cardiac trauma, cardiac surgery, and endomyocardial biopsy);
– CNS (central nervous system) trauma;
– brain tumor;
– subarachnoid hemorrhage;
– organ rejection (heart transplant);
– amyotrophic lateral sclerosis (ALS);
– convultions, status epilepticus and muscle spasms;
– acute psychosis with agitation;
– pulmonary embolism;
– Reye’s syndrome;
– after strenuous exercise, intramuscular injection;
– renal failure and hemodialysis;
Increased levels of CK also can be found in case of viral myositis, polymyositis, and hypothyroidism.
Carbon monoxide poisoning and alcohol abuse may also elevate the level of CK-MB in the serum.
Increased CK-BB is characteristic for:
– atresia (biliary);
– cancer (breast, gastrointestinal, prostatic, widespread malignancies);
– cerebrovascular accident (hemorrhage, infarction);
– intestinal necrosis;
– malignant hyperthermia;
– renal failure;
Decreased level of CK is found in case of the muscle atrophy due to metastatic injury and connective tissue diseases. This change may also be seen in Addison’s disease, anterior pituitary hyposecretion, connective tissue disease, hepatic disease (alcoholic), low muscle mass, and during the first half of the pregnancy. Steroids may also be involved.
Reduced CK-BB can be seen in patients with Huntington disease, multiple sclerosis, and amyotrophic lateral sclerosis.
CK may be ordered along with other blood chemistry tests – electrolytes, or creatinine (to evaluate kidney function). A urine myoglobin test may also be performed.
The test requires a blood sample, which is drawn by putting a needle into a vein in the arm.