Creatine Kinase (CK)

About the Test

Purpose of the test

A CK test may be used to detect:

• Myositis a group of diseases characterized by inflammation of muscles. Symptoms include difficulty in standing, moving about, swallowing or breathing, and/or muscle pain.
• Myopathies a result of damage due to muscle disorders such as muscular dystrophy
• Rhabdomyolysis the destruction or degeneration of muscle tissueas seen in extreme heat exposure, physical exertion, or crush injuries. Symptoms include muscle cramps, aches, dark urine, and feeling weak or tired. Repeat testing may be required to see if the CK level rises.
• A second heart attack that occurs shortly after the first, though the troponin tests are the main way to diagnose an initial heart attack

A series of CK tests may be used to monitor muscle damage to see if it resolves or continues. CK consists of three subunits (isoenzymes): BB (CK-1; found primarily in brain; when CK-BB is present in the blood, it is released from smooth muscles, including those in intestines, uterus, or placenta), MB (CK-2; found primarily in heart muscle), and MM (CK-3; found primarily in skeletal muscle). Testing for these isoenzymes can be useful when the muscle damage source is unclear.

CK may be ordered along with other blood chemistry tests such as electrolytes, BUN, or creatinine (to evaluate kidney function). Myoglobin is found in muscles and can be released as a result of muscle damage. A urine myoglobin may also be ordered and will reflect the degree of damage – the more myoglobin present the greater the damage. Excess myoglobin can be toxic to kidneys.

What does the test measure?

A CK test measures the amount of CK in the blood. While a small amount of CK is normal, primarily from skeletal muscles, elevated levels might indicate muscle damage.

When should I get this test?

A CK test may be ordered when muscle damage is suspected and at regular intervals to monitor for continued damage. It may be ordered when a muscle disease (myopathy) such as muscular dystrophy is suspected, or if you have experienced physical trauma, such as crushing injuries or extensive burns.

Doctors might also order a CK test if you have ongoing symptoms associated with muscle injury such as:

• Muscle or joint pain
• Muscle weakness
• Frequent falling
• Swelling feet/legs
• Dark urine

CK tests can also be ordered if you take a certain kind of drug, such as a statin, that has been linked with potential muscle damage.