A creatine kinase (CK) test may be used to detect inflammation of muscles (myositis) or serious muscle damage and/or to diagnose rhabdomyolysis if a person has signs and symptoms, such as muscle weakness, muscle aches, and dark urine. The urine may be dark because of the presence of myoglobin, another substance released by damaged muscles that can be harmful to the kidneys. CK may be ordered by itself or along with other blood chemistry tests such as electrolytes, BUN or creatinine (to evaluate kidney function). A urine myoglobin may also be ordered.
A person may have muscle injury with few or nonspecific symptoms, such as weakness, fever, and nausea, that may also be seen with a variety of other conditions. A health practitioner may use a CK test to help detect muscle damage in these cases, especially if someone is taking a drug such as a statin, using ethanol or cocaine, or has been exposed to a known toxin that has been linked with potential muscle damage. In those who have experienced physical trauma, a CK test may sometimes be used to evaluate and monitor muscle damage.
The CK test may be ordered if a person has chest pain or other symptoms that lead a doctor to suspect heart damage. This assay was once one of the primary tests ordered to help diagnose a heart attack, but in the U.S., this use of CK has been largely replaced by troponin. The CK test may sometimes be used to help detect a second heart attack that occurs shortly after the first.
A series of CK tests may be used to monitor muscle damage, including heart damage, to see if it resolves or continues. If a CK is elevated and the location of the muscle damage is unclear, then a health practitioner may order CK isoenzymes or a CK-MB as follow-up tests, to distinguish between the three types (isoenzymes) of CK: CK-MB (found primarily in heart muscle), CK-MM (found primarily in skeletal muscle), and CK-BB (found primarily in the brain; when present in the blood, it is primarily from smooth muscles, including those in intestines, uterus or placenta).
A CK test may be ordered whenever muscle damage is suspected and at regular intervals to monitor for continued damage. It may be ordered when someone has experienced physical trauma, such as crushing injuries or extensive burns. The test may be ordered when a person has symptoms associated with muscle injury such as muscle pain or weakness and when a person has nonspecific symptoms, especially when taking a drug or after an exposure to a substance that has been linked with potential muscle damage.
The CK test may sometimes be ordered when a person has chest pain and a heart attack is suspected. It may be ordered after a heart attack has been diagnosed to monitor for ongoing heart damage.
A high CK, or one that goes up from the first to the second or later samples, generally indicates that there has been some recent muscle damage but will not indicate its location or cause. Serial test results that peak and then begin to drop indicate that new muscle damage has diminished, while increasing and persistent elevations suggest continued damage.
People may have CK levels that are significantly to greatly increased, depending upon muscle damage severity. Those who have rhabdomyolysis may have CK levels that are as much as 100 times normal levels.
Chest pain and increased CK levels indicate that it is likely that a person has recently had a heart attack. Levels that drop, then rise again may indicate a second heart attack and/or ongoing heart damage.
Normal CK levels may indicate that there has not been muscle damage or that it occurred several days prior to testing.
Moderately increased CK levels may be seen following strenuous exercise such as in weight lifting, contact sports, or long exercise sessions.
This article was last reviewed on February 25, 2013. | This article was last modified on February 24, 2015.
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