High creatine kinase (CK) levels are often the first sign of muscle damage in neuromuscular disorders like Duchenne muscular dystrophy (DMD). DMD is a form of muscular dystrophy that causes progressive muscle damage and muscle weakness. CK is an enzyme released into the blood when muscles are damaged.

It’s important to understand what CK is and how living with DMD can affect CK levels over time. Your or your child’s health care provider can monitor CK levels to help diagnose DMD, assess how the disease is progressing, and guide treatment options like corticosteroid therapy or participation in clinical trials.

How Does DMD Cause Muscle Damage?

DMD causes muscle damage because of a lack of a structural muscle protein called dystrophin, a protein that helps keep muscles strong and protects them from injury. Dystrophin is encoded by the DMD gene located on the X chromosome.

People with DMD have a deletion, duplication, or other mutation (change) in the dystrophin gene. The dystrophin gene contains directions for how your body should make dystrophin. In DMD, the mutation disrupts these instructions. As a result, the body produces less than 5 percent of the amount of dystrophin protein needed for muscles to work properly.

The dystrophin protein is a key structural protein in muscles. It helps to strengthen muscle fibers and protect them from damage. Without dystrophin protein, the muscle fibers become damaged and die over time.

What Is Creatine Kinase?

Creatine kinase is an enzyme (a type of protein) found inside muscle cells that helps muscles produce energy. CK is mostly found in skeletal muscles (the muscles that move the body) and the heart muscle, though some CK is also found in the brain. Different types of CK are in these tissues:

• CK-MM is skeletal muscle.
• CK-MB is in the heart muscle.
• CK-BB is in the brain.

Normally, CK stays inside muscle cells to help make energy for the cell. However, if muscle cells become damaged, the cells break open and release CK into the bloodstream.

A health care provider may take a blood sample to check levels of CK if they suspect a muscle disorder — such as DMD or Becker muscular dystrophy — or muscle injury. The blood test to check CK levels is called a CK test, though it may also be referred to as a creatine phosphokinase test or CK total test.

What Causes High CK Levels?

Most CK in the body stays inside muscle cells. When CK levels in the blood are high, it usually means there’s been recent, significant muscle damage. However, a CK test alone cannot reveal the specific cause of muscle degeneration (weakening and loss). Many things can raise CK levels, including:

• Myopathies (muscle diseases)
• Muscle inflammation
• Intense physical exercise
• Severe burns
• Electrocution
• Bacterial infection of the muscle
• Delirium tremens (severe alcohol withdrawal)
• Brain injury

If an injury is the cause, follow-up CK tests will show lower CK levels over time as the muscles heal. CK levels that remain high after repeat testing may suggest a chronic (long-term) condition. DMD is one example of a chronic myopathy that can cause persistently high CK levels. In DMD, the lack of dystrophin protein leads to muscle damage, which releases CK into the blood.

When Are CK Levels Checked?

A CK test is often one of the first steps in diagnosing neuromuscular diseases like DMD.

CK tests aren’t usually included in routine checkups for children. A health care provider may order one if a child shows developmental delays or muscle weakness. Developmental delays happen when a child takes longer than expected to reach milestones like sitting up, standing, or walking. Children with DMD may also show other signs that prompt CK testing, such as:

• Frequent falls
• Walking with legs apart or on the toes
• Gower’s sign (using the hands to push on the legs to stand up)
• Trouble lifting the head or neck
• Delayed speech
• Enlarged calf muscles
• Scoliosis (a curved spine)

Additional Testing for High CK Levels

High CK levels alone aren’t enough to diagnose DMD. Your health care provider may order additional tests to help confirm the diagnosis.

One common test is a liver enzyme test. Muscle breakdown, like that seen in DMD, can cause high levels of liver enzymes. In people with DMD, elevated liver enzymes usually don’t mean there’s a problem with the liver itself.

If CK levels are high, genetic testing is needed to confirm a DMD diagnosis. Genetic testing involves looking at the DNA to check for mutation in the dystrophin gene.

If genetic testing doesn’t find any genetic mutations, a muscle biopsy can help by checking dystrophin protein levels in the muscle tissue. During a muscle biopsy, a small piece of muscle tissue is surgically removed and then examined under a microscope. While this test can provide useful information, it isn’t necessary for a DMD diagnosis.

For families with a family history of neuromuscular conditions, genetic counseling can guide testing and help determine whether mutations in the DMD gene are present.

Talk to your health care provider about which additional tests are needed if your child has high CK levels.

How Does DMD Affect CK Levels?

Young children with DMD will typically have elevated CK levels. A child with DMD can have high CK levels before any symptoms appear. High CK levels can also be seen in newborns with DMD. The highest CK levels usually occur between ages 2 and 5.

A normal CK level for a child without DMD between the ages of 0 to 3 years is 60 to 305 units per liter. A child with DMD can have a CK level 50 to 200 times higher than normal levels.

The exact value of what’s considered a normal versus an elevated CK level may differ depending on the laboratory that runs the test. Other factors can also affect what’s considered a normal CK level. In general, people assigned male at birth and those with higher muscle mass have higher CK levels, according to Cleveland Clinic. Your health care provider can help you understand the results of your child’s or your CK test.

CK Levels May Decrease Over Time With DMD

After the CK level peaks, it will usually fall about 25 percent each year and may eventually return to a normal level. Because DMD is a progressive disease, you might expect that CK levels would remain elevated throughout the course of the disease. However, CK levels don’t always correlate with muscle function. CK levels are often highest when a child has more muscle function. In fact, decreasing CK levels are associated with declining motor function.

CK levels are highest in the early stages of DMD because muscle damage happens more rapidly, and there is more muscle tissue to break down. As the disease progresses, damaged muscle tissue is replaced by fat and scar tissue instead of new muscle. Since CK is released only from muscle tissue, less available muscle means lower CK levels over time.

Talk to your health care provider about how often your child should have a CK test to monitor DMD progression.

Talk With Others Who Understand

On myMDteam, the social network for people living with muscular dystrophy and their loved ones, members come together to ask questions, give advice, and share their experiences with life and care challenges related to MD.

Does your health care provider regularly monitor you or your child’s CK levels? How have your CK levels changed over time? Share your story in the comments below, or start a conversation by posting on your Activities page.