Monoclonal gammopathy of uncertain significance (MGUS)

Last updated Nov. 2, 2025, 3:36 a.m. by ivo

Monoclonal gammopathy of undetermined significance (MGUS) happens when abnormal white blood cells make abnormal proteins called M proteins. M proteins don’t usually cause issues. Most people with MGUS don’t have symptoms. But a small percentage of people with this condition may develop blood cancer or a more serious blood disorder.

MGUS is a blood disorder where your plasma cells make an abnormal protein (M protein). Blood and urine (pee) tests can detect this protein. Usually, M proteins don’t cause issues, and most people with MGUS don’t have any symptoms from the protein.

Healthcare providers consider MGUS a “benign precursor” to a blood cancer called multiple myeloma or one of several other conditions. This means that although MGUS isn’t cancer, it can become one. The language can be confusing. But most people with MGUS don’t develop serious disease.

Still, as there’s a chance that MGUS can progress, your healthcare provider will monitor your condition. If you’ve been diagnosed with MGUS, talk with your provider about how often you should be monitored and what tests you’ll need.

Symptoms and Causes

Symptoms of MGUS

This condition rarely causes symptoms. You may not know you have MGUS until a routine blood test or urine test reveals you have M proteins.

MGUS causes

This condition happens when your bone marrow makes abnormal plasma cells. A plasma cell is a type of white blood cell. Normally, individual plasma cells produce antibodies. Antibodies are proteins that defend your body against germs.

In MGUS, abnormal plasma cells produce M proteins instead of the antibodies you need. Doctors don’t know why your body makes abnormal plasma cells in the first place.

Risk factors

MGUS is more common in people aged 50 and older. The risk of developing it increases with age. Starting at age 50, people have a 2% to 3% chance of developing this condition. People aged 70 and older have a 5% chance. You may be more likely to develop MGUS if you:

Are Black
Are male
Have a close relative with MGUS or a blood cancer
Have a history of exposure to pesticides or insecticides
Have a history of autoimmune diseases
Have been exposed to high levels of radiation
Have served in the military

Complications of this condition

About 20 to 25 out of 100 people with MGUS develop a serious blood disorder, like multiple myeloma. Not all people with MGUS develop it, but all people with multiple myeloma have MGUS first.

MGUS sometimes progresses to conditions like:

Amyloidosis
Chronic lymphocytic leukemia
Waldenstrom macroglobulinemia

MGUS can increase your risk of:

Blood clots
Bone loss or fracture
Infections
Kidney issues
Problems with the nerves throughout your body (peripheral neuropathy)

Diagnosis and Tests How doctors diagnose this condition Providers diagnose MGUS by analyzing your blood and urine for signs of M protein. They also assess risk factors to see how likely it is that MGUS will become cancer or a serious blood disorder. These factors include: The amount of M protein in your blood: Levels higher than 1.5 grams per deciliter (g/dL) indicate more risk. The type of M protein in your blood: There are different kinds of immunoglobulin (Ig) M proteins. Some are more likely to progress to a serious condition. The amount of free light chains in your blood: Serum-free light chains (FLC) are proteins that plasma cells make. Serum FLC tests can detect abnormal concentrations of free light chains. People at risk according to all three factors are more likely to develop blood cancer. People who don’t have any risk factors have little risk of developing it. Management and Treatment How is MGUS treated? Most people with this condition don’t need treatment. Instead, your healthcare provider will monitor M protein levels in your blood. Sometimes, they’ll check a urine sample regularly, depending on how high the M protein levels are. This is called watchful waiting, or active surveillance. For example, if you have higher levels of proteins, your provider may check your blood work every three to six months for the first year. Then, your provider may recommend checking your blood less often. You may need tests every six to 12 months for signs of cancer or another condition that may need to be treated. If you have bone loss, your provider may recommend medications and other steps to improve bone density. When should I see my healthcare provider? If you have MGUS, your healthcare provider will let you know how often to come in for tests. You should also reach out if you start noticing symptoms. Signs and symptoms of more serious conditions in people who have MGUS include: Anemia Bone pain Dizziness Easy bruising or bleeding Fatigue Headaches Hearing or vision loss Night sweats Rashes or other skin conditions Tingling or numbness Unexplained weight loss

Outlook / Prognosis

What can I expect if I have this condition?

In general, most people with MGUS don’t have symptoms. Many never need treatment. A small percentage of people develop certain blood cancers or blood disorders that do require treatment with pills or other medications.

If blood and urine tests show M proteins, you’ll need regular blood and urine tests at least every six to 12 months. That way, your healthcare providers can watch for signs that MGUS is becoming a serious condition.

It’s unclear how MGUS impacts a person’s life expectancy. But screenings after a MGUS diagnosis improve survival rates for people who develop multiple myeloma.

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