Cardiac enzymes are protein molecules released into the blood stream from heart muscle damaged by a blocked artery. This is known as a heart attack. When someone is admitted to the hospital with a clear cut heart attack, these enzymes are measured to get an idea of how much muscle was damaged.
Many people are admitted to the hospital with apparent heart symptoms but other tests such as the EKG are inconclusive about whether a heart attack (i.e., damage to the heart muscle) actually occurred. In these cases, the cardiac enzymes are used to determine if this was a heart attack as opposed to a bad episode of angina or perhaps symptoms unrelated to the heart altogether.
The enzymes most commonly measured these days are creatinine phosphokinase (CPK) (also known as creatinine kinase (CK)) and Troponin. Like any other test in medicine, these tests are not perfect.
These enzymes have a characteristic rise and fall pattern after a heart attack. It may take 4 hours or more after the onset of symptoms for the test to become abnormal and up to 24 hours for the level to peak. Consequently, blood test are taken from the patient several times. A normal blood test upon arrival in the emergency room does not mean a heart attack has not occurred. Eventually, the levels in the blood fall back to normal. (Credit to Sharon Kumm, University of Kansas School of Nursing)
