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

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 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, 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). This paraprotein does not do anything useful, and for most people it does not cause any problems.

Each year, about 1 out of 100 people with MGUS (1%) develop a related cancer. So most people with MGUS never develop a cancer because of it, or need any 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 in the MGUS and predict whether it is likely to change in the future.

Causes of MGUS

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 by mistake. Some autoimmune disorders may slightly increase the risk of developing MGUS. These include lupus and pernicious anaemia.

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 (peripheral neuropathy), 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 test you for MGUS if a paraprotein is found in your blood following 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 a number of different 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 in blood disorders (haematologist). Not everybody who has MGUS is referred to a haematologist. Your doctor decides if this is needed based on your symptoms and test results. As well as tests, your doctor may physically examine you 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 cell (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. 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. The nurses will explain more about how to do this test.


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.


Occasionally body scans, such as MRI or 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 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 after this your blood tests are normal 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 more tests for you.

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 natural 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 needed.