The cardiac enzyme creatine kinase is a bodily enzyme that rises in level in the bloodstream following injury to the heart muscle, explains WebMD. In addition to creatine kinase, a medical test called a cardiac enzyme study also measures the levels of troponin I and troponin T, two proteins.
There are usually only low levels of creatine kinase, troponin I and troponin T in the blood, notes WebMD. Normally, these enzymes and proteins exist in the heart muscle cells as well as in the cells of some other bodily tissues. Damage to the heart muscle causes them to leak into the bloodstream, so a cardiac enzyme study is useful in determining whether a patient has had a heart attack or sustained another form of heart trauma. However, because the enzymes and proteins also exist in other tissues, their levels can also rise in response to damage elsewhere in the body. For this reason, the doctor must consider the patient's symptoms and results of other tests, such as an electrocardiogram, to determine whether the results of a cardiac enzyme study indicate heart damage has occurred.
Doctors order cardiac enzyme studies when patients have symptoms that suggest they are having a heart attack or are at risk of a heart attack in the near future, states WebMD. These symptoms may include chest pain, difficulty breathing, sweating and nausea. Doctors may also run cardiac enzyme studies if they are concerned about potential heart damage due to an infection.