Description

Creatine Kinase Test

Creatine kinase is an important enzyme needed for energy production and muscle function. Athletes have more of this enzyme in their blood, but so do obese and overweight people. High levels can tell us if there is muscle, heart, or brain damage. Keep reading to learn more about this enzyme, what it means if your levels are high or low, and how to address irregular values.

What is Creatine Kinase?

Creatine kinase (CK), also known as creatine phosphokinase, is an enzyme that plays a role in energy production. Higher amounts of this enzyme are found in tissues that use a lot of energy, such as the muscles (including the heart) and the brain.

Creatine kinase will leak into the blood when these tissues are damaged. That’s why blood levels of this enzyme can tell us whether there has been tissue damage, i.e. a heart attack, stroke, sports injury, or muscle disease.

If your creatine kinase levels are high, your doctor may order a creatine kinase isoenzyme tests to determine which type of creatine kinase enzyme is high..

• CK-MM: muscles
• CK-MB: heart
• CK-BB: brain

Normal Range

There is still no universally agreed upon range for creatine kinase. Different laboratories have different normal ranges, reported in U/L (units per liter) or ukat/L (microkatals per liter).

People who have greater muscle mass have higher CK levels. That is why men usually have higher CK values than women.

The low normal limit for both men and women is approximately 20 – 30 U/L (0.34 – 0.51 ukat/L). The upper normal limit for men is anywhere from 200 to 395 U/L (3.4 – 6.8 ukat/L) and for women, it’s up to 207 U/L (3.52 ukat/L)

CK levels are around 70% higher in healthy African Americans, compared to people of European descent! Some studies indicate that healthy black men and women can have significantly higher values than the currently recognized normal range(s) – up to 712 and 323 IU/L, respectively

High Creatine Kinase Levels

Elevated CK points to recent tissue damage. However, it doesn’t point to a cause or the location of the damage.

It is possible to be healthy and have higher CK levels. As mentioned above, people of African descent can have up to 70% higher CK levels than healthy Caucasians [6, 5, 7].

Your doctor will interpret this test, taking into account your medical history and other test results, and will repeat it if necessary.

Furthermore, a “falsely high CK” due to exercise or other strenuous physical activity is very common. In a large community study of over 12,000 people in Norway, people who had elevated CK levels were re-tested after 3 days of rest. CK levels returned back to normal in 70% of the cases [8].

To ascertain that the rise in CK is due solely to exercise or exclude physical activity as a factor, the test should be repeated after a week of rest (i.e. 7 days without exercise).

If elevated CK persists, it is more likely to be due to an underlying health issue. People who have elevated creatine kinase due to an underlying health issue may experience the following symptoms…

• Muscle weakness
• Cramps
• Muscle pain
• Fatigue
• Inability to exercise (due to pain or weakness)
• Dark urine

Causes of High Creatine Kinase Levels

Causes shown below are commonly associated with elevated creatine kinase. Work with your doctor or another health care professional to get an accurate diagnosis.

1) Exercise/Training

Exercise and training are the main cause of increased creatine kinase levels

CK levels transiently increase to over 30 times the upper normal limit within 24 hours of strenuous physical activity and then slowly decline back to normal over the next 7 days. To what degree CK spikes depends on the type and duration of exercise.

Studies have shown that even stretching can increase CK

Also, people who are untrained will experience greater spikes in CK levels due to greater muscle damage.

On the other hand, athletes have higher resting CK levels compared to non-athletes. A study of over 700 athletes suggests that normal reference ranges for athletes may be over two times higher than normal ranges: 82 – 1,083 U/L in men and 47 – 513 U/L in women.

Fun fact: The highest creatine kinase on record was over a million and was caused solely by a heavy workout 

2) Obesity

Although higher CK levels are found in athletes, conversely, high CK levels are also found in obese and overweight people.

In a study of 1,444 subjects, higher CK levels were linked with higher BMI and waist-to-hip ratio.

In another study of over 10,000 adults, overweight and obese men had almost 2 times greater odds of having elevated CK.

Similarly, in 4,500 people, CK levels were higher in people with greater body mass.

Scientists may have found an explanation for this. They discovered that obese and overweight people have more fast-twitch (type II) muscle fibers and less slow-twitch (type I) muscle fibers. Fast-twitch muscle fibers have higher CK activity