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(Monoclonal gammopathy of undetermined significance)

Your doctor may have told you that you have ‘MGUS’, which stands for monoclonal gammopathy of undetermined significance.


This is a blood condition that affects cells in your bone marrow. It isn’t cancer, and people diagnosed with it don’t have any symptoms. You may have been diagnosed following blood tests for something else.

Although MGUS isn’t harmful by itself, a small number of people diagnosed with it (about 1% per year) go on to develop blood cancer. This means if you are diagnosed with MGUS, you will be routinely monitored.

What causes MGUS?


Everyone has a type of white blood cell made in the bone marrow called plasma cells. These plasma cells create antibodies, which help to fight infection.

In people with MGUS, some of their plasma cells start producing too much of one type of antibody, even though there isn’t an infection to fight. These abnormal antibodies, called paraproteins or M-proteins, don’t do anything useful, and for most people don’t cause any problems.

We don’t know why people develop MGUS, although we do know that it is more common in certain groups:

  • Older people – it’s rare for anyone under the age of 40 to develop MGUS

  • Black ethnicity

  • Men

  • People with a close family member who has MGUS may be more at risk

  • People with some autoimmune diseases may be slightly more at risk

How is MGUS diagnosed?


People with MGUS do not have symptoms, so the condition is often picked up during routine blood tests, or tests for something else.

Your doctor might suspect MGUS if paraproteins show up in a blood test. These can also be a sign of a more serious condition, like blood cancer, and you may need to have further tests to rule these out. Your doctor may refer you to a haematologist (a clinician who specialises in blood disorders) for these tests, but this isn’t always necessary and you may instead be monitored by your GP.

Alongside blood tests, you may have a urine test, a CT scan, an MRI scan or a bone marrow biopsy. These will help your doctor understand why the paraproteins have been found in your blood and help them make a diagnosis.

If I have MGUS,
will I develop WM?


Being diagnosed with MGUS doesn’t mean that you will develop blood cancer or another blood condition.

There are three categories of MGUS:

  • non-IgM MGUS (including IgG, IgA and IgD)

  • IgM MGUS

  • Light Chain (LC) MGUS

All carry a small risk of developing into another blood condition for which you might need treatment.

If you’ve been diagnosed with IgM MGUS, there is a chance that this might develop into WM, or less commonly another form of low-grade lymphoma, or extremely rarely, IgM myeloma. However, the risk for MGUS developing into a form of cancer is very low.

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Living with MGUS


Because of the small risk of developing other blood conditions, you’ll be monitored by your doctor. This will include routine blood tests to check your paraprotein levels. These might start at frequent intervals but as time goes by, your doctor may decide that you don’t need them as frequently. The frequency will depend on your individual circumstances, including your overall health, risk of developing a more serious condition and results of investigations.

It’s important to look out for symptoms that could suggest your MGUS is developing into something more serious.

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If you experience any of the following, be sure to tell your doctor so they can check you over:

  • Repeated infections

  • Fatigue

  • Weakness or breathlessness

  • Fevers and night sweats

  • Unexplained weight loss

  • Swollen glands, lumps or masses

  • Blurring or loss of vision

  • Dizziness or headaches

  • Poor concentration or confusion

  • New or constant bone pain

  • Numbness or tingling (pins and needles) in fingers or toes

  • Bruising or bleeding easily

  • Progressive ankle or leg swelling

Support for people with MGUS


Because MGUS is often diagnosed when you are being tested for something else, or even through routine blood tests, your diagnosis may come as a bit of surprise, and you may have lots of questions.

It’s also perfectly natural to feel worried about what this means for your health and your future. It’s important to remember that most people with MGUS don’t go on to develop Waldenstrom's macroglobulinaemia or any other blood condition, and live symptom-free.

If you are feeling anxious, talk to your nurse or doctor. They will be able to talk things over with you and may arrange counselling if you need it.

WMUK is also here to support you. You can call or email us anytime, whether you have questions or need to talk through any worries. Contact us.

Man and women sitting in a circle during a support group meeting
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