Dr Charles Shepherd, Hon. Medical Adviser, ME Association.
At present there is no diagnostic blood test for ME/CFS – but testing your blood is essential to rule out other illnesses that can cause similar symptoms.
Dr Shepherd talks about what blood comprises, the kind of tests employed by researchers, what clinical tests should be taken to rule out misdiagnosis and what those tests can reveal.
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Introduction: What does a blood test measure?
Human blood contains red cells, white cells, platelets and plasma:
- Red blood cells carry oxygen around the body – so a deficiency or abnormality here will probably cause anaemia.
- White blood cells help the body to fight off infections and respond to allergies. White cells are sub-divided into cells called basophils, eosinophils, lymphocytes and neutrophils. Each cell has a slightly different function and an increase in a specific cell type can indicate than an allergic or infective reaction is taking place.
- Platelets help to form blood clots and prevent bleeding. So, a platelet deficiency can cause excessive or prolonged bleeding from a wound site.
- Plasma is the fluid component that contains a wide variety of substances produced by the immune system (e.g. antibodies, cytokines, natural killer cells) as well as enzymes, hormones and proteins that are made by or excreted by various organs and tissues in the body. The plasma also contains all the other chemicals and substances – vitamins, minerals, sugars and fats – that are carried around the body.
The use of new investigative technologies means that scientists can now also look at specific proteins (proteomics), metabolites – the remains of chemical reactions that have taken place (metabolomics) – and genetic factors that may predispose people to developing specific diseases (genomics).
These tests are increasingly being employed by researchers who are looking for the cause of ME/CFS. They are also being used to try and find diagnostic blood markers (biomarkers), or markers for sub-groups, such as people with severe ME/CFS.
Laboratory analysis of a small sample of blood can, therefore, reveal a great deal of basic information about your state of health and the function of various organ systems.
Is there a diagnostic blood test for ME/CFS?
While minor blood test abnormalities can occur in ME/CFS, none of them are sufficiently consistent or robust enough to turn them into diagnostic markers in our current state of knowledge.
So, the simple answer here is ‘no’ and a diagnostic ‘ME blood test’ seems unlikely to be made available in the near future.
The search for a diagnostic biomarker for ME/CFS
Significant progress is however being made in the search for potential diagnostic biomarkers and a number of research groups have been reporting some interesting preliminary findings.
The UK ME/CFS Biobank (which is funded by the MEA Ramsay Research Fund) has found that some people with severe ME/CFS have a lower than normal level of a muscle enzyme called creatine kinase.
They have also published results from a big study on the immunology of ME/CFS that was funded by the National Institutes of Health in America. This study found that some people with ME/CFS have an increased proportion of an immune system component called MAIT cells (mucosal associated invariant T cells).
This is an interesting abnormality that is being linked to neurological and autoimmune conditions such as multiple sclerosis and inflammatory bowel disease, where these cells appear at sites of inflammation in the nervous system and gut lining.
The Stanford research group in America have reported on changes in the shape of red blood cells and more recently observed that when a specific type of immune cell is stressed to increase its energy requirements it reacts in a different way to immune cells from healthy controls.
Before drawing any firm conclusions about these findings, they need to be repeated in larger numbers of people with ME/CFS, and by other independent research groups, and compared to findings in people with autoimmune, infective and neurological conditions, as well as people with unexplained chronic fatigue.
Summaries and reviews of all these recent research studies can be found in the Research section of the MEA website.
Which blood tests should be checked before a diagnosis of ME/CFS is confirmed?
Everyone should have a number of routine blood tests before a diagnosis of ME/CFS is confirmed. The results of all of these tests should be within normal limits. So, the main purpose of arranging all these blood tests is to help the doctor to rule out medical conditions that can also produce fatigue and other ME/CFS-like symptoms.
Continues with a list of appropriate blood tests to aid diagnosis, blood tests for children, when to repeat blood tests, and a detailed explanation of what each blood test means.
Images sources: 123RF/AlexanderRaths/SergiyLukutin
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