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Monoclonal gammopathy of unknown significance (MGUS)

What is MGUS?

Monoclonal gammopathy of unknown significance (MGUS) is characterised by the presence of an abnormal protein in the blood that is produced by plasma cells. Plasma cells are cells in the bone marrow that normally produce antibodies to fight infection.

The abnormal protein produced by the MGUS plasma cells is called either an M–protein or paraprotein. This abnormal protein is found in the blood and is monoclonal. Monoclonal means that it is being produced by one family of cells that are all identical copies of each other.

MGUS can be referred to as a benign condition as there is only a small risk that MGUS can develop into myeloma or a related blood disorder. The average risk of progression to active myeloma is about 1% per year. Lifelong monitoring to detect any increase in the paraprotein level and development of symptoms is required.


The risk of MGUS increases as you get older. About 3% of people age 50 and older and 5% of people aged 70 and older have M protein in their blood. The highest incidence is among adults aged 85 and older.


The cause of MGUS is unknown.


There are rarely any symptoms associated with MGUS.


The condition is usually detected incidentally during a routine check-up when a blood test shows an increase in the blood protein level. The diagnosis is then confirmed by having a particular blood test called a serum electropheresis test which identifies the abnormal antibody.

Clinical features

MGUS has a number of clinical features. These include having a low level of protein (less than 30g/l) and less than 10 per cent plasma cells in the bone marrow: There is no damage to bones, calcium levels are normal, little or no protein is present in the urine, the kidney’s function normally and there is no anaemia.

Treatment and monitoring

MGUS does not require any active treatment, however monitoring is recommended.  Monitoring of MGUS includes regular clinical assessment and follow up measurements of serum protein. The serum protein should be checked after 3 months and then again at 6 months to establish a firm diagnosis of MGUS.

If the paraprotein has remained stable it may be checked annually thereafter.