Creatine kinase (CK) formerly known as creatine phosphokinase is primarily found in muscle cells including the heart, striated muscles and the brain. The normal range of creatine kinase for men is 38 – 174 units/L and for women 96 – 140 units/L. Men typically have more muscle mass than women which accounts for the higher range values. African Americans have been found to have a higher normal range for creatine kinase as well.
The test procedure measures the amount of optical change that occurs as the enzyme, creatine kinase, acts upon the substrate, in this case, creatine. An increase in the creatine kinase level means that there has likely been damage to the muscles. Whether this is smooth muscle, such as heart muscle or striated muscle, such as the long muscles of the legs is determined by the physician through evaluating the patient’s symptoms, recent history and other laboratory testing.
What Do Increased Creatine Kinase Levels Mean?
Elevated creatine kinase indicates muscle damage, or in some cases, over-exertion of muscles such as in lifting weights. The physician can determine through physical examination the possibility of heart attack versus a disease of the skeletal muscles. Further laboratory testing in the case of a probable heart attack includes a CK-MB test and a Troponin Test.
Total creatine kinase is comprised of isoenzymes related to different types of muscle. They are CK-MB (specific for the heart), CK-MM, (specific for skeletal muscle), and CK-BB (specific for brain and lung tissue). Elevations of any of the three isoenzymes will increase the total creatine kinase. Laboratory tests in which there is an elevated total creatine kinase will prompt the physician to order a CK-MB if symptoms of a heart attack exist.
The CK-MB test determines the portion of total creatine kinase that is related to the heart muscle. In addition to total creatine kinase and CK-MB testing, Troponin levels are measured. Troponin is one of the first chemical changes that are measurable following a heart attack and allow more rapid diagnostics which improve the prognosis for the patient.
Following damage to muscle, as in a heart attack, for example, the creatine kinase levels will gradually rise. Testing of changes over a twenty-four hour period is typically done to determine if patients have experienced a heart attack and to ascertain the severity of the attack.
Troponin increases more rapidly and begins its descent more quickly. Troponin is a good indicator of whether or not a heart attack has actually occurred and of the severity of the attack. This coupled with the total creatine kinase provide very important information as to how long the recovery process will be for the patient as well as the quality of life that can be expected following recovery.