What is creatine kinase (CK)?

Creatine kinase (CK) is an enzyme found in skeletal muscle as well as in the heart, brain and other tissues. Increased amounts of CK are released into the blood when there is muscle damage.1 Elevated CK levels reflect muscle damage in patients with Duchenne muscular dystrophy, making it an important diagnostic marker for the condition.2

When to order a CK test

A CK test should be carried out if:

  • Examination and medical history suggest progressive muscle weakness1,3,4
  • A child has delayed motor function, such as not walking well or not able to rise to stand by 18 months1,3,5,6
  • A child shows developmental delay, including delays with mixed presentation (e.g. speech and cognition), and evaluation suggests a peripheral neuromuscular problem3
  • A child has a positive family history of Duchenne muscular dystrophy and suspicion of abnormal muscle function6
  • Blood tests reveal an unexplained increase in transaminases6

What the results mean1,6

IF CK IS ELEVATED
(Normal range is generally up to 250 U/L*)1
Refer to neuromuscular specialist for Duchenne muscular dystrophy gene testing6
IF CK IS NORMALDoes not rule out other neuromuscular disorders1

Developmental delay should trigger a CK test

Normal or mildly elevated CK levels do not rule out neuromuscular disease1

*The normal CK range is generally up to 250 U/L. Absolute values may differ between laboratories.1

Prompt CK testing can help to achieve the correct diagnosis and bring reassurance to families1,9

1. National Task Force for Early Identification of Childhood Neuromuscular Disorders. Guide for primary care providers. Available at: https://childmuscleweakness.org/wp-content/uploads/2019/05/PrimaryCareProviderPacket.pdf [last accessed November 2020].
2. van Ruiten HJ, et al. Arch Dis Child. 2014,99:1074–1077.
3. Lurio JG, et al. Am Fam Physician. 2015;91:38–44.
4. Chakrabarty T, et al. Arch Dis Child Educ Pract Ed. 2020;105(3):157–163.
5. WHO Multicentre Growth Reference Study Group. Acta Paediatr. 2006;450:86–95.
6. Birnkrant DJ, et al. Lancet Neurol. 2018;17:251–267 [Part 1].
7. Centers for Disease Control and Prevention. Developmental milestones. Available at: https://www.cdc.gov/ncbddd/actearly/pdf/checklists/all_checklists.pdf [last accessed November 2020].
8. Aartsma-Rus A, et al. J Pediatr. 2019;204:305–313.e14.
9. Dubrovsky AL. EMJ Neurol. 2018;6:64–67.

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