Monoclonal gammopathy of unknown significance (MGUS) is a blood condition in which a person's body makes too many of the same type of protein that fight infections.

The blood has a large number of different proteins called the plasma proteins. One type of protein is called gamma globulin. Normally, many different types of gamma globulin are made to fight different infections. When most of the protein being made is all from cells of the original (clone) gamma globulin protein, this is called monoclonal gammopathy. Most people with MGUS have a low monoclonal protein level.

Generally, MGUS does not cause symptoms or major health problems. It is often found by chance when lab tests are done for other reasons, such as to measure the level of protein in the blood. Monoclonal antibodies can attach to nerves and cause numbness, tingling, and weakness. Most people with MGUS are fine for many years and do not need any treatment. In some cases MGUS can change and progress to a cancer, such as multiple myeloma, macroglobulinemia, or B-cell lymphoma.

People who have MGUS may need a physical exam, blood tests, and urine tests two times a year to see if it is progressing to cancer so that treatment can be started early.