Question

I was interested to read about the new research study from the ME Biobank that looked at the results from all the common blood tests that should be arranged before a diagnosis of ME is made. This study found that people with severe ME often have a reduced blood level of creatine kinase (CK) – something that I also have. But when I asked my doctor to explain why I was told that it was ‘nothing to worry about’. So what is creatine kinase? And why do people with severe ME have a reduced level of CK in their blood?

Answer

This test measures the amount of creatine kinase (CK) in the blood. CK is an enzyme that is found in the heart, brain, skeletal muscle and other tissues. So increased amounts are released into the bloodstream when there is inflammation or damage involving these tissues, the muscle in particular. Any condition that causes muscle damage and/or interferes with muscle energy production can therefore cause an increase in CK levels.

For example, inflammation of muscles, called myositis, can increase CK. And rhabdomyolysis, a severe breakdown of skeletal muscle tissue that causes muscle pain, tenderness, weakness and swelling, is associated with significantly elevated levels of CK. Of relevance to ME/CFS is the fact that statins (drugs for lowering cholesterol) can cause this type of muscle damage – so they need to be used with care. People who develop a greater muscle mass also have higher than normal levels. Exercise such as running or cycling can increase CK concentrations.

Interestingly, a 1988 study that examined CK levels in muscle biopsies from people with a post-viral fatigue syndrome found elevated levels of CK. These people were less severely affected and closer to the onset of symptoms than those in a subsequent study from the ME/CFS Biobank – so the raised level might be related to an initial viral infection causing muscle inflammation.

The 2019 ME/CFS Biobank study – see extract below – was the first to report low levels of CK in people with severe ME/CFS. The reason why this is occurring is uncertain – it may just be a marker of lowered levels of muscle activity in people who are not mobilising. However, low levels of creatine kinase have been found in an autoimmune condition called SLE (Lupus) – where it has been linked to the level of inflammation – and research studies suggest that there is an autoimmune component to ME/CFS.

In this analytical cross-sectional study, we aimed to explore potential haematological and biochemical markers for ME/CFS, and disease severity. We reviewed laboratory test results from 272 people with ME/CFS and 136 healthy controls participating in the UK ME/CFS Biobank (UKMEB).

After corrections for multiple comparisons, most results were within the normal range, but people with severe ME/CFS presented with lower median values of serum creatine kinase, compared to healthy controls and non-severe ME/CFS. The differences in CK concentrations persisted after adjusting for sex, age, body mass index, muscle mass, disease duration, and activity levels compared to controls.

This is the first report that serum CK concentrations are markedly reduced in severe ME/CFS, and these results suggest that serum CK merits further investigation as a biomarker for severe ME/CFS.

Nacul L et al. Evidence of Clinical Pathology Abnormalities in People with ME/CFS from an Analytic Cross-Sectional Study | April 2019

More information

• Lab Tests Online: Creatine Kinase (CK) Test | April 2019 (updated March 2020).