MGUS (monoclonal gammopathy of unknown significance) is a non-cancerous (benign) condition in which large amounts of a type of antibody are produced in the body. This antibody is called a paraprotein (or M-protein).

MGUS doesn’t usually cause any symptoms. It is usually diagnosed with blood and urine tests. But you may have other tests to rule out more serious conditions. These may include x-rays, scans and occasionally, a bone marrow test.

Most people with MGUS remain well and treatment is not necessary. But a small number of people may go on to develop cancers, such as myeloma (cancer of the plasma cells) and lymphoma (cancer of the lymphatic system). This means that everyone with the MGUS must have regular check-ups.

What is MGUS?

MGUS is a non-cancerous (benign) condition. Most people with MGUS remain well. However, a small number of people may go on to develop more serious problems, so everyone with the condition has regular tests.

MGUS (monoclonal gammopathy of unknown significance) is a condition where the body makes an abnormal protein, called a paraprotein. These paraproteins are found in the blood and urine when they’re tested.

MGUS is linked to the immune system. The immune system helps the body fight infection and disease. It is made up of organs such as the bone marrow, the spleen, lymph nodes and white blood cells.

MGUS affects plasma cells. Plasma cells are a type of white blood cell that make antibodies to help fight infections. Antibodies are made from a protein called immunoglobulin.

With MGUS, some plasma cells make an abnormally high number of a type of antibody called a paraprotein (or M-protein). This paraprotein doesn't do anything useful, and for most people it isn't harmful.

Although MGUS is not a cancer, people who have it are at slightly higher risk of certain cancers. The two main cancer types people with MGUS are more at risk of developing are myeloma (cancer of the plasma cells) and lymphoma (cancer of the lymphatic system).

These cancers also produce large amounts of paraproteins. Although the levels of paraprotein are raised in MGUS, they're not as high as the levels in people with cancer.

Most people with MGUS remain well and it causes few problems. Because a small number of people may go on to develop cancer, everyone with MGUS has regular checks.

Causes of MGUS

MGUS is a rare condition that becomes slightly more common as people get older. The cause is unknown. It's more common in people with conditions that affect the immune system, such as rheumatoid arthritis and certain infections.

Signs and symptoms of MGUS

MGUS is usually found during a blood test carried out for some other reason. It doesn't usually cause any symptoms.

Occasionally, people with MGUS have numbness or tingling in their hands and feet, or problems with their balance. This may be due to damage to nerves (peripheral neuropathy) caused by the paraprotein in the blood.

If these symptoms are troublesome, or get worse, you may be referred to a neurologist (a doctor who specialises in conditions of the nervous system).

Diagnosing MGUS

You will be usually be seen by a haematologist (a doctor who specialises in treating blood disorders). The haematologist may examine you and ask you questions about your general health.

You will usually have blood and urine tests. Your haematologist may also advise you to have other tests to check for myeloma or lymphoma. These tests may include x-rays, scans and, occasionally, a bone marrow test. The bone marrow is where blood cells are made and develop until they’re ready to go into the blood.

Not everyone will need to have these tests and your haematologist will advise you on which are appropriate for you.

Blood tests

You have a blood test called serum protein electrophoresis to diagnose MGUS. This test is also used to check on MGUS. This test measures the type and amount of paraprotein produced by the plasma cells.

You will also have a test to check the number of different types of blood cells (full blood count). This is to make sure your bone marrow is working well

Your doctor may arrange blood tests to check how well your liver and kidneys are working. You may also have your calcium levels checked, as these can be raised in myeloma.

Urine tests

You will be asked to give samples of your urine, which will be checked for paraproteins.


Some people may have x-rays taken of different bones in the body. This is to check for damage to the bones, which can be caused by myeloma.

CT scan (computerised tomography)

A CT scan takes a series of x-rays, which build up a three-dimensional picture of the inside of the body. It is used to find out if lymph nodes, or organs such as the liver or spleen, are enlarged. The scan takes 10-30 minutes and is painless. It uses a small amount of radiation, which is very unlikely to harm you and will not harm anyone you come into contact with.

You will be asked not to eat or drink for at least four hours before the scan. You may be given a drink or injection of a dye, which allows particular areas to be seen more clearly. This may make you feel hot all over for a few minutes. It’s important to let your doctor know if you are allergic to iodine or have asthma, because you could have a more serious reaction to the injection.

Bone marrow sample

In some situations, the haematologist may recommend that a sample of bone marrow is taken (biopsy) to be examined under a microscope.

A doctor or nurse takes a small sample of bone marrow from the back of the hip bone (pelvis). Before the bone marrow sample is taken, you’ll be given a local anaesthetic injection to numb the area. You may also be offered a short-acting sedative to reduce any pain or discomfort during the test.

You’ll be asked to lie on your side. The doctor or nurse then passes a needle through the skin into the bone and draws a small sample of liquid marrow into a syringe (bone marrow aspirate). It can feel uncomfortable for a few seconds when the liquid marrow is drawn into the syringe. After this, they take a small core of marrow from the bone (a trephine biopsy). A small plaster or dressing is placed over the skin.

You may feel bruised after having a sample of bone marrow taken, and have an ache for a few days. This can be eased with mild painkillers.

The test is usually done as an outpatient and takes about 15-20 minutes.

Treatment and follow-up for MGUS

MGUS doesn't need treatment as it doesn't usually cause any symptoms. In most people, MGUS remains stable and may never cause any problems. However, because of the small risk of MGUS developing into a cancer, such as myeloma or lymphoma, regular check-ups are important. Always contact your doctor between check-ups if you develop any of the following symptoms:

  • new constant bone pain in one area (such as in the back, ribs, hip or pelvis)
  • unexplained weight loss
  • increasing breathlessness
  • extreme tiredness (fatigue)
  • having different infections one after the other, caused by not having enough healthy white blood cells.

You will usually have a blood test to check your paraprotein levels every 3-4 months for the first year. This can be done by your own GP or your haematologist.

Your doctors will monitor the pattern of the paraprotein levels - whether they stay roughly the same at each check, or are gradually rising. If the paraprotein level remains steady and there are no other problems, the time between your appointments will become longer.

If the paraprotein levels are rising, or if you have symptoms, tests may need to be repeated or new tests may be carried out.

Useful organisations

Leukaemia CARE

Leukaemia CARE is a national group promoting the welfare of people with leukaemia and other blood disorders. It can provide information on MGUS.

The Lymphoma Association

The Lymphoma Association gives emotional support, advice and information on all aspects of lymphoma. It has a national network of people with lymphoma and local groups.

Myeloma UK

Myeloma UK provides information and support to people affected by myeloma. It helps to improve treatments through research, education and awareness.

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