What is creatine kinase (CK)?

Creatine kinase (CK) is present in many tissues including the heart, brain, and skeletal muscle. CK is sometimes included as part of a health screen to investigate signs of muscle damage and high levels in the blood can indicate recent muscle damage. 

This guide explains what CK is, what it can tell you about your health, and why we no longer offer testing for CK. 

• What is creatine kinase (CK)?
• What is the difference between creatine, creatinine, and CK?
• Why do I need a CK test?
• Why do we not routinely measure CK?
• What is a normal CK level?
• What causes a high CK level?
• What causes a low CK level?
• How can I lower my CK levels?
• What should I do if my CK levels are abnormal?
   

What is creatine kinase (CK)?
 

Creatine kinase (CK), not to be confused with creatinine, is an enzyme found in the body, particularly in skeletal muscle, heart muscle, and the brain [1]. Damage to muscle cells can cause CK to spill into the bloodstream, which can be detected with a blood test.  

CK is needed for energy processes in the body. It facilitates the reaction that allows energy to be stored and released when it’s needed [1]. 

The three main types of CK enzymes are:  

• CK-MM - found mainly in skeletal muscle 
• CK-MB - found mainly in heart muscle 
• CK-BB - found mainly in brain tissue 
   

What is the difference between creatine, creatinine, and CK?
 

Creatine is a compound involved in the supply of energy for muscular contractions. It’s made in the liver, kidneys, and pancreas and gets transported to skeletal muscle, where it helps to supply energy. It’s sometimes taken as a supplement to increase muscle mass and performance.  

Creatinine is a waste product that’s made when creatine is broken down by the body. It’s processed by the kidneys, which help to filter it out of the body into the urine. Because of this, creatinine is used as a marker of kidney function.  

Creatine kinase is an enzyme found mostly in muscle cells. It facilitates the reaction that converts creatine into an energy store. This is the marker that can indicate muscle damage. 
 

Why do I need a CK test?
 

A CK test is usually requested by your doctor when there is reason to suspect muscle injury or damage. You may have symptoms of muscle aches or weakness. Occasionally, CK-MB (found in the heart muscle) levels may be used to detect a heart attack. 
 

Why do we not offer testing for CK?

We no longer offer testing for creatine kinase (CK) as it can be affected by a wide range of lifestyle factors, including exercise and diet. Other factors such as minor illnesses (such as flu) and minor injuries can cause high readings of CK. Because of this, it is quite common for high levels to be found, even though there may be no significant underlying cause. Abnormal CK results can cause unnecessary worry for our customers and may result in unneeded GP appointments. So, we have taken the decision to remove it from our routine tests.  
 

What is a normal CK level?
 

In a healthy adult, a normal CK level varies according to several different factors, including sex, ethnicity, and level of physical activity.  

A normal CK level is approximately [2]: 

• 40 – 320 U/L for men 
• 25 – 200 U/L for women 

Levels may be up to 70% higher in people of African descent compared with Caucasians [3]. Some studies indicate that healthy black men and women can have significantly higher values than currently recognised normal ranges — up to 712 and 323 IU/L respectively [4, 5]. CK is often also higher in people with a muscular build.  

After trauma, CK levels can begin to rise within two to twelve hours but may not peak for up to two days after certain injuries. Therefore, you may need to have serial measurements to assess the trend.  
 

What causes a high CK level?
 

Anything that causes significant muscle damage can cause a raised CK level. It’s most often raised due to strenuous exercise or as a side effect of statin therapy.  

Causes of raised CK include [6]: 

• Direct damage to muscle — strenuous exercise, recent surgery, labour, trauma, seizures, or a prolonged period on the floor following a fall 
• Cardiac damage — heart attack or myocarditis (inflammation of the heart muscle) 
• Side effects of medicines — statins, antiretrovirals, beta-blockers and other blood pressure medications, clozapine, and colchicine 
• Endocrine disorders — underactive or overactive thyroid 
• Genetic conditions — muscular dystrophies (a group of progressive conditions that gradually cause the muscles to weaken) 
• Autoimmune conditions — polymyositis dermatomyositis(a group of rare conditions that cause weak or painful muscles), and less commonly, rheumatoid arthritis, coeliac disease, and lupus 
• Being overweight or obese [7] 

If your levels are raised, and you believe it may be due to exercise, it’s worth repeating the test after a period of rest to make sure it’s resolved. Levels can increase to up to 30 times the upper normal limit with strenuous activity but will gradually decline to normal over seven days or so.  
 

What causes a low CK level?
 

As CK levels reflect total muscle mass, frailty, or being confined to bed rest for extended periods may lead to lower values. 

Causes of low CK include:  

• Low muscle mass 
• Autoimmune disease — including lupus and rheumatoid arthritis [8, 9] 
• Pregnancy — CK levels may be reduced in the second trimester of pregnancy [10] 
   

How can I lower my CK levels?
 

Elevated CK can be a sign of serious tissue damage or an underlying disease. It’s important to identify the cause with your doctor first and then treat any underlying condition. 

Review medications 

Statins, such as atorvastatin, will rarely cause muscle inflammation (myositis). If you develop muscle aches after starting a statin you should discuss this with your doctor. A creatine kinase test may be used to check for muscle inflammation. If you have severe symptoms or your creatine kinase is very high your doctor might advise you to stop the statin. 

Some people develop symptoms of muscle pain or weakness (myalgia). This is a common side effect and is usually mild.  

Resting after strenuous exercise 

If your CK is raised due to muscle damage after exercise, there are some steps you can take to improve muscle recovery: 

• Eat plenty of carbohydrates, protein, and antioxidants after your workout [11] 
• Incorporate recovery periods in your training regimen 
• Consider massage therapy which is proven to reduce muscle soreness [12] 
   

What should I do if my CK result is abnormal?

If your result is borderline raised and you have no symptoms, it is likely nothing to worry about, especially if you are a fit and active individual. It’s worth repeating your result in a few weeks to make sure your result has returned to normal. 

If you’re concerned, or if your result is very raised, it’s best to discuss this with your GP who can investigate this with you. 

References

1. Cabaniss CD. Creatine Kinase. 1990. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 32. Available from: https://www.ncbi.nlm.nih.gov/books/NBK352/
2. South Tees Hospitals NHS Foundation Trust. 2021. Creatine kinase (CK) - South Tees Hospitals NHS Foundation Trust. [online] Available at: <https://www.southtees.nhs.uk/services/pathology/tests/creatine-kinase-ck-cpk/> [Accessed 24 March 2022].
3. Brewster, L. M., Coronel, C. M., Sluiter, W., Clark, J. F., & van Montfrans, G. A. 2012. Ethnic differences in tissue creatine kinase activity: an observational study. PloS one, 7(3), e32471. https://doi.org/10.1371/journal.pone.0032471
4. Lilleng H, Johnsen SH, Wilsgaard T, Bekkelund SI. Are the currently used reference intervals for creatine kinase (CK) reflecting the general population? The Tromsø Study. Clin Chem Lab Med. 10;50(5):879-84. doi: 10.1515/CCLM.2011.776. PMID: 22070220.
5. George, M. D., McGill, N. K., & Baker, J. F. 2016. Creatine kinase in the U.S. population: Impact of demographics, comorbidities, and body composition on the normal range. Medicine, 95(33), e4344. https://doi.org/10.1097/MD.0000000000004344
6. Moghadam-Kia, S., Oddis, C. V., & Aggarwal, R. 2016. Approach to asymptomatic creatine kinase elevation. Cleveland Clinic journal of medicine, 83(1), 37–42. https://doi.org/10.3949/ccjm.83a.14120
7. Haan, Yentl & Oudman, Inge & Diemer, Frederieke & Karamat, Fares & van Valkengoed, Irene & Montfrans, Gert & Brewster, L. 2016. Creatine kinase as a marker of obesity in a multi-ethnic population. Molecular and Cellular Endocrinology. 442. 10.1016/j.mce.2016.11.022.
8. Sanmartí R, Collado A, Gratacós J, Herrera BE, Font J, Cañete JD, Orellana C, Muñoz-Gomez J. Reduced serum creatine kinase activity in inflammatory rheumatic diseases. J Rheumatol. 23(2):310-2. PMID: 8882037.
9. Lee YH, Choi SJ, Ji JD, Song GG. Serum creatine kinase in patients with rheumatic diseases. Clin Rheumatol. 19(4):296-300. doi: 10.1007/s100670070049. PMID: 10941812.
10. Chemnitz G, Nevermann L, Schmidt E, Schmidt FW, Lobers 1979. Creatine kinase (EC-No.2.7.3.2) and creatine kinase isoenzymes during pregnancy and labor and in the cord blood. Clin Biochem. 12(6):277-81. doi: 10.1016/s0009-9120(79)80128-9. PMID: 535161.
11. Luden ND, Saunders MJ, Todd MK. Postexercise carbohydrate-protein- antioxidant ingestion decreases plasma creatine kinase and muscle soreness. Int J Sport Nutr Exerc Metab. 17(1):109-23. doi: 10.1123/ijsnem.17.1.109. PMID: 17460336.
12. Guo, J., Li, L., Gong, Y., Zhu, R., Xu, J., Zou, J., & Chen, X. 2017. Massage Alleviates Delayed Onset Muscle Soreness after Strenuous Exercise: A Systematic Review and Meta-Analysis. Frontiers in physiology, 8, 747. https://doi.org/10.3389/fphys.2017.00747