CK (Creatine Kinase)

What is CK (creatine kinase)?

Creatine kinase, known for short as CK or CPK, is an enzyme involved in energy production in cells. It helps muscles obtain energy quickly, especially during sudden, intense movements that require strength. It is found in the highest amounts in skeletal muscles, and to a lesser extent in heart muscle and the brain. When muscle cells are damaged, this enzyme passes from the cells into the blood and its level in the blood rises.

The CK test determines total creatine kinase activity in the blood, and the result is given in U/L. The enzyme has three subtypes: CK-MM, which predominates in skeletal muscle; CK-MB, which is more concentrated in heart muscle; and CK-BB, which is found in the brain. Total CK alone does not show which muscle the enzyme comes from; when necessary, subtypes such as CK-MB are examined separately.

When is the CK test ordered?

CK is one of the basic tests used to investigate and monitor muscle damage or muscle diseases. Your doctor may also order it when symptoms appear in people taking certain medicines that can cause muscle pain. In people diagnosed with a muscle disease, it may be repeated at regular intervals to monitor the course of the disease.

CK is also an important indicator for the early detection of serious muscle breakdown, which can develop after a severe injury, after lying immobile on the floor for a long time or after very intense exercise. In such cases, the doctor also evaluates kidney function at the same time.

• Unexplained muscle pain, cramps or muscle weakness
• Muscle symptoms that appear while taking cholesterol-lowering medicines
• Suspected muscle damage after a fall, crush injury or major trauma
• Dark urine after intense exercise
• Monitoring of muscular dystrophy or inflammatory muscle diseases
• Accompanying muscle symptoms when the thyroid gland is underactive

How should you prepare for the CK test?

You do not need to fast for the CK test. However, intense exercise, heavy lifting, long-distance running and injections into the muscle can raise CK levels for several days. For this reason, it is recommended that you avoid strenuous physical activity for two days before the test and mention it if you have recently had an intramuscular injection.

Some medicines, particularly cholesterol-lowering drugs, can affect CK; tell your doctor about the medicines you take and do not stop them on your own. Mentioning recent events such as surgery or a fall also makes interpretation easier. The blood sample is taken from the arm, and the procedure takes a few minutes. At times when you find it hard to move around, having our nurse take this sample at your home or workplace lets you get tested without going out.

What does the CK result mean?

High CK indicates that there is damage in the muscles; however, it does not explain the cause on its own. Mild increases after intense exercise, an intramuscular injection or a minor injury are usually temporary. Marked increases, on the other hand, may be associated with muscle inflammation, muscular dystrophies, drug-induced muscle damage, an underactive thyroid gland or a serious form of muscle breakdown called rhabdomyolysis.

In rhabdomyolysis, substances released from the muscles into the blood can damage the kidneys, so very high CK values may require urgent evaluation. Low CK, by contrast, usually has no clinical significance and may be seen in people with low muscle mass. Reference ranges may vary by laboratory, age, sex and even ethnic background; this page shows the ranges set for men and for women by the laboratory that performs the analysis. The significance of your CK result should be determined by your doctor, who evaluates your symptoms and your other tests together.