MGUS (monoclonal gammopathy of unknown significance) is a non-cancerous condition. People with MGUS make an abnormal protein, called a paraprotein or M-protein, which is found in the urine or blood.

The paraprotein does not usually cause any problems or symptoms. It is usually found by chance when a person is having blood tests for another reason. Several other conditions can also cause paraproteins in the blood. Doctors need to do further tests to rule these conditions out before diagnosing MGUS. These tests may include x-rays, scans and a bone marrow test. The tests may be arranged by your GP, or you may be referred to a haematologist (a doctor who specialises in treating blood disorders).

People with MGUS do not usually need any treatment. But there is a small risk of MGUS developing into a blood cancer, such as myeloma (cancer of the plasma cells) or lymphoma (cancer of the lymphatic system). Because of this, your doctor may recommend you have regular blood tests to check for any changes in the MGUS.

What is MGUS?

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

MGUS is not a cancer, but people who have it are at 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, a type of white blood cell. 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). This paraprotein doesn't do anything useful, and for most people it does not cause any problems.

Causes of MGUS

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

Signs and symptoms of MGUS

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

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

Diagnosing MGUS

Doctors may suspect a person has MGUS if a paraprotein is found in their blood following a blood test. A paraprotein in the blood can also be a sign of more serious conditions, including myeloma or lymphoma. Doctors usually need to do several tests to rule out these other conditions before they can diagnose MGUS.

Tests to diagnose MGUS may be arranged by your GP, or you may be referred to a haematologist (a doctor who specialises in treating blood disorders). As well as tests, the doctor may physically examine you and ask questions about your health.

Some of the following tests may be used:

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 cell (full blood count).

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 myeloma can cause increased calcium levels.

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.


You may have body scans such as CT (Computerised Tomography) or MRI (Magnetic Resonance Imaging). Your doctor or specialist nurse can give you more information if they think you need one of these.

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 will take a small sample of bone marrow from the back of the hip bone (pelvis). Before the bone marrow sample is taken, you will 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 will be asked to lie on your side. The doctor or nurse will then pass a needle through the skin into the bone and draw 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 will take a small core of marrow from the bone (a trephine biopsy). A small plaster or dressing is then 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 to 20 minutes.

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 can cause certain symptoms. Always contact your doctor if you develop any of these symptoms:

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

If you have MGUS, your doctor may also recommend that you have ongoing blood tests, similar to those you had at diagnosis. One of these blood tests will check the paraprotein level in your blood.

In the first year, blood tests may be done every 3 to 4 months. After this, if your blood tests are normal and you do not have any new symptoms, you will 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 further tests.

Not everyone with MGUS will need ongoing follow-up with blood tests. For some people, the chance of MGUS ever causing a problem in their lifetime is so small that no further checks are needed. But it is still important to tell your doctor if you develop any of the symptoms mentioned above.

Useful organisations

Myeloma UK

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

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.

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