Creatine kinase

Creatine kinase (S-CK) is an enzyme, or a protein, that mainly occurs in the muscles, such as skeletal and heart muscles. Lower concentrations of creatine kinase also occur in the brain, uterus, and intestines. There are three forms (isoenzymes) of creatine kinase, based on their locality: muscle isoenzyme, heart isoenzyme and brain isoenzyme.

Usually, low amounts of creatine kinase are released from skeletal muscle cells into the blood, from which its concentration can be measured. When muscle is damaged, more creatine kinase is released into the bloodstream. The greater the muscle damage, the higher the CK value. Men typically have higher muscle mass than women, and therefore the reference range is higher in men.

When should creatine kinase levels be measured?

Testing creatine kinase is a good idea when suspecting muscle damage or muscle inflammation. A muscle disease can be the result of an accident, such as from staying still for a long time on a hard surface because of a stroke, a fit, or drunkenness. This condition is known as rhabdomyolysis. In this case, the concentration of creatine kinase in the blood increases strongly. The condition also involves the urine turning red due to myoglobin ending up in the urine. Myoglobin is the substance responsible for the colour of muscle cells, and normally muscles can store oxygen in it.

Creatine kinase can also increase as a result of intensive physical exercise, muscle surgery, inflammation, or myocardial infarction.

Muscle disease can also be caused by rarer diseases. Symptoms of muscle disease include muscle weakness and sensitivity.

What does a creatine kinase test measure?

The test indicates whether the creatine kinase enzyme is leaking from the cells into the bloodstream. However, the cause of the leak has to be examined by means of other tests.