Creatine phosphokinase, or CK or CPK, is an enzyme found in the brain, heart and skeletal muscles. A physician will commonly order a CPK test to determine whether a person has suffered a heart attack. There are different types of CPK and a physician uses this information to interpret abnormal results.
A CPK test requires a blood sample. To collect a blood sample, a technician will commonly apply a tourniquet above the site of collection, most commonly on the inside of the elbow. The technician will then insert a small needle into the vein and collect the sample. The technician will remove the tourniquet, apply pressure to the collection site and apply a bandage. There is very little risk in collecting the sample, though technicians may need to apply pressure longer for patients who use blood thinners.
Abnormal results vary greatly depending upon many factors including age, gender, testing methods and sample population. A physician will determine whether the result of the test is abnormal based on these factors along with symptoms. An elevated CPK level simply means that damage to muscle has occurred somewhere in the body. In suspected heart attack patients, an elevated level from the time of admittance to the second or third test can indicate that a heart attack has occurred.
Physicians often find high CPK levels in patients who have damage to the brain, heart or skeletal muscle. This can occur in such conditions as a heart attack, a brain injury, a stroke, convulsions, inflammation of the heart muscle, electrical shock, lung tissue death or muscular dystrophy. In some cases, people with thyroid conditions or a condition known as rhabdomyolysis, a condition in which damaged muscles leak a protein called myoglobin into the bloodstream, may cause an elevated CPK, according to MedlinePlus, a publication of the National Institutes of Health.
For patients who arrive at the emergency room with a suspected heart attack, a technician will draw blood for CPK levels upon arrival and again at four and six hours to determine whether there has been an increase in CPK levels, according to Lab Tests Online. If levels have increased over the six hours, a physician will often order a more specific blood test known as a troponin test to see if the heart muscle is damaged. Other follow-up tests may include urine analysis, kidney function studies, imaging studies and further blood tests.
People with greater muscle mass or who exercise heavily or for long periods have higher levels of CPK than those who do not. African-Americans may have higher levels of CPK than other ethnicities. Muscle damage from an injury may also cause an elevated level of CPK as well as many medications including statins used for cholesterol. Early pregnancy can cause lower levels of CPK, according to Lab Tests Online.