What is MGUS?

MGUS stands for monoclonal gammopathy of unknown significance. It is a non-cancerous condition where the body makes an abnormal protein, called a paraprotein.

Although MGUS is not a cancer, people with it have a slightly higher risk of developing:

  • myeloma (a cancer of blood cells called plasma cells)
  • lymphoma (a cancer of blood cells called lymphocytes).

MGUS affects plasma cells. These are a type of white blood cell made in the bone marrow. Normal plasma cells make proteins called antibodies to help fight infections. With MGUS, some plasma cells make an abnormal type of antibody called a paraprotein (or M protein). For most people, this does not cause any problems.

Each year, about 1 out of 100 people with MGUS (1%) develop a related cancer, such as myeloma or lymphoma. However, most people with MGUS never develop a related cancer and do not need treatment.

Doctors do not know why some people with MGUS develop a cancer and others do not. Your doctor may do regular blood tests to help check for any changes and predict whether the MGUS is likely to change in the future.

MGUS causes

Doctors do not know what causes MGUS, but different things are known to increase the risk of it developing.


MGUS is more common in older people. It is rare in people under the age of 40.


MGUS is more common in black people than in white people.


MGUS is almost twice as common in men than in women.

Family history

People who have a close family member (such as a parent, brother or sister) with MGUS have a slightly increased risk of developing it.

Autoimmune disease

Autoimmune diseases cause the body’s immune system to attack healthy cells in the body. Some may slightly increase the risk of developing MGUS.

These include:

  • lupus – a condition when the immune system attacks your own tissues and organs
  • pernicious anaemia – low levels of red blood cells caused by not having enough vitamin B12 in the body.

MGUS symptoms

MGUS does not usually cause any symptoms. But a small number of people with MGUS have problems with their balance, or numbness or tingling in their hands and feet. This is called peripheral neuropathy. Symptoms may be because of damage to their nerves caused by paraproteins in the blood.

People with nerve problems may be referred to a neurologist. This is a doctor who specialises in conditions of the nervous system.

Some people may also have problems with the kidneys.

Diagnosing MGUS

As MGUS does not usually cause symptoms, it is often found when having tests for other possible health problems. Doctors may test you for MGUS if a paraprotein is found in your blood after a blood test. A paraprotein in the blood can also be a sign of more serious conditions, such as myeloma or lymphoma. Doctors may need to do tests to rule out these other conditions before they can diagnose MGUS.

Your GP may arrange these tests, or you may be referred to a doctor who specialises in blood disorders. They are called a haematologist. Not everybody who has MGUS is referred to a haematologist. It will depend on your symptoms and test results. Your doctor may also need to do a physical examination and ask some questions about your health.

You may have some of the following tests.

  • Blood tests

    You will have a blood test that measures the amount and type of paraprotein made by the plasma cells. You will also have a test to check the number of different types of blood cells. This is called a full blood count.

    Your doctor may arrange blood tests to check how well your liver and kidneys are working. This is to check your general health, but also because myeloma can affect these organs. You may also have your calcium levels checked, as myeloma can cause increased calcium levels.

  • Tests on your urine

    Some types of paraprotein can be found in the urine (pee). You may be asked to give samples of your urine to check for these. You may need to take a container home and collect your urine for 24 hours. This is because larger samples can provide more information. The nurses will explain more about how to do this test.

  • X-rays

    Your doctor may arrange for you to have some x-rays. This is to check for damage to the bones, which can be caused by myeloma.

  • Scans

    Sometimes, body scans, such as MRI or PET-CT scans, are done instead of x-rays.

  • Bone marrow test

    Some people may have a sample of bone marrow taken (biopsy) to be examined under a microscope.

    A doctor or specialist nurse takes a small sample of bone marrow from the back of the hip bone (pelvis). The sample is sent to a laboratory to be checked for abnormal cells. This is done to look for myeloma cells in the bone marrow.

Treatment and follow-up for MGUS

MGUS does not usually need treatment as it rarely causes any symptoms. In most people, MGUS remains stable and never causes any problems.

There is a small risk of MGUS developing into a cancer, such as myeloma or lymphoma. If this happens, it is usually a slow-growing lymphoma. This can cause certain symptoms. Always contact your doctor if you have any of these symptoms:

  • new or constant bone pain (such as in the back, ribs, hip or pelvis)
  • different infections, one after another, that need antibiotics to treat them
  • feeling short of breath
  • extreme tiredness (fatigue)
  • unexplained weight loss
  • night sweats
  • new lumps or swellings.

Your doctor may also recommend you have regular blood tests. These will be like the ones you had at diagnosis.

In the first year, you may have blood tests every few months. If your blood tests are normal after this time and you have no new symptoms, you have blood tests less often.

If you have new symptoms or blood tests show changes, such as a rising paraprotein level, your doctor may arrange for you to have more frequent tests.

Not everyone with MGUS needs regular follow-up appointments and blood tests. For some people, the chance of it causing problems in their lifetime is so small, no checks are needed. But it is still important to tell your doctor if you get any of the symptoms mentioned above.

Your feelings about MGUS

If you are told you have MGUS and need further tests, it is normal to feel worried. But most people with MGUS do not go on to develop cancer. Talk to your doctor if you feel anxious a lot. They can explain more about your risk and arrange counselling for you if you feel it might help.

Macmillan is also here to support you. If you would like to talk, you can do the following:

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About our information

  • References

    Below is a sample of the sources used in our myeloma information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    National Institute for Health and Care Excellence (NICE). Myeloma: diagnosis and management. NICE guideline [NG35]. Published: 10 February 2016 Last updated: 25 October 2018. Available from: https://www.nice.org.uk/guidance/ng35/chapter/recommendations Accessed: 19/07/22

    Jonathan Sive et al., on behalf of the British Society of Haematology. British Journal of Haematology. Guidelines on the diagnosis, investigation and initial treatment of myeloma: a British Society for Haematology/UK Myeloma Forum Guideline. Published: 21 March 2021 Available from: https://onlinelibrary.wiley.com/doi/10.1111/bjh.17410 Accessed: 19/07/22

    M.A. Dimopoulos et al. Annals of oncology. European Society for Medical Oncology (ESMO). Multiple myeloma: EHA-ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Volume 32, ISSUE 3, P309-322, March 01, 2021. Available from: https://www.annalsofoncology.org/article/S0923-7534(20)43169-2/fulltext Accessed: 19/07/22

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Anne Parker, Consultant Haematologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

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Date reviewed

Reviewed: 01 September 2021
Next review: 01 September 2024
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

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