Creatine kinase (CK or CPK) is an enzyme or type of protein found in muscle and brain that leaks out and is released into the bloodstream when muscle is damaged. In normal conditions, there is very little creatine kinase circulating in the blood of the average, healthy human being.
CK is the most sensitive enzyme and in the presence of most diseases, levels can be elevated as much as 50 to 100 times the reference level.
Progression of skeletal muscle atrophy is one of the characteristic features in cancer patients. Even in paraneoplastic disorders the serum CK level typically is elevated 8-100 times normal.
Skeletal muscle atrophy is a common comorbidity of cancer. Progression of skeletal muscle atrophy is one of the characteristic features in cancer patients and the progressive depletion of skeletal muscle is a hallmark of many types of advanced cancer.
Guillain-Barré syndromeis a disorder caused by "nerve" inflammation (not muscle inflamation), involving progressive muscle weakness or paralysis. GBS initially does not usually produce evidence of muscle inflammation or waisting such as elevation of Creatine Kinase (CK) concentration. Persons with GBS or clinically similar disorders typically have normal or low CK levels at onset of the disease, unless tissue damage in the brain or elsewhere has already occurred.
To illustrate, a low/normal CK at the time of a patient's admission to hospital would argue favourably against a diagnosis of structural brain damage, or active metastatic cancer.
A clinical feature of demyelination is muscle weakness without muscle atrophy. Persons with Muscular Dystrophy, Guillain-Barré Syndrome and other neuromuscular disorders typically have low creatine kinase levels.
Lyme disease may also cause weakness secondary to peripheral neuropathy but it too does not produce evidence of muscle inflammation such as elevation of the CK.
Creatine Kinase (CK) should typically not be elevated in GBS and if it is, another cause (or underlying disorder) should be suspected.
The highest creatine kinase activities are found in skeletal muscle, myocardium and brain tissue. Significantly increased creatine kinase levels may support a hypothesis of brain death; normal CK levels do NOT.
In females, total Creatine Kinase should be 10-79 units per liter (U/L). CK is the most sensitive enzyme and in the presence of most diseases, levels can be elevated as much as 50 to 100 times the reference level.