What Does CK Mean in a Blood Test?

Oh, the wonderful world of lab tests! So many letters, abbreviations, and confusing numbers. For example, if you’ve recently complained of chest pain, or if your doctor thinks you could have a muscle disease, they may have ordered a lab test called a CK. What does CK mean in blood test results?

CK is an abbreviation for creatine kinase - also known as CPK - or phosphocreatine kinase. Creatine kinase is a muscle enzyme found in three different types in the human body. In skeletal muscle it’s in the form of CK-MM, in the brain, CK-BB, and in the heart muscle, CK-MB. These forms are known as isoenzymes.

Total CK levels go up whenever there’s an injury to muscle - and the CK-MB form of creatine kinase rises when there’s injury specifically to the heart muscle – usually due to a heart attack.

The total CK rises in blood test results when skeletal muscle is injured or damaged. In this case, the type of creatine kinase that goes up is the CK-MM form. A doctor usually orders a CK level when he or she suspects a disease involving muscle tissue like muscular dystrophy or inflammatory muscle diseases such as dermatomyositis and polymyositis.

Creatine kinase can also be elevated in certain neurological diseases that affect muscle tissue such as ALS or Guillain Barré syndrome. An underactive thyroid or parathyroid gland, located in the neck, can cause high CK levels too.

An elevated CK level can have a variety of other etiologies as well. Certain medications – particularly statin drugs used to treat elevated cholesterol – can cause elevations in creatine kinase. When CK levels are many times above normal and a person is taking statins, it may mean a person has a serious form of muscle injury called rhabdomyolysis, which can be life-threatening.

Creatine kinase levels on blood testing can also be transiently elevated after intense exercise, after an intramuscular injection, after a fall or electrical shock, as the result of a viral infection, after a seizure, and due to malignancy. In these cases, CK levels are usually elevated less than five times normal and goes down quickly once the situation resolves.

Some normal people have creatine kinase levels that are consistently higher than normal. This is more common in African-Americans, bodybuilders, and people with large, bulky muscles. Elevated CK levels are also more common in certain families. In these cases, it’s important to rule out other causes before assuming the elevation isn’t due to muscle problems.

An elevated CK level on a blood test usually needs further evaluation and testing. If a person is experiencing chest pain and CK-MB is high, it can be a sign of heart damage due to heart attack. This elevation is usually transient and returns to normal in a few days. A high CK level can also be a sign of muscle disease, damage, or injury. Less commonly, it can be elevated for benign reasons such as vigorous exercise or due to genetics.

A high CK gives a clue that something may be wrong with the muscles, but further testing is needed to make the final diagnosis.

Medscape.com. "Clinical Approach to Muscle Diseases: Laboratory Approach in the Evaluation of a Suspected Myopathy”

Merck Manual. Eighteenth edition. 2006.

Lab Tests Online. “CK”.