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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.
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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.
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Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
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.
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.
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.
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:
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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:
MGUS can increase your risk of:
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:
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.
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.
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:
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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.
Monoclonal gammopathy of undetermined significance (MGUS) is a bit of a medical mystery. There are quite a few things we still don’t know. For example, healthcare providers don’t know why some people never develop serious disease, while others do. But researchers are working to unravel some of the mystery. For instance, your provider may be able to predict if you’ll develop serious medical issues. This can take a lot of the guesswork out of this diagnosis. And it can help ease your mind knowing that you’ll get the screenings you need to get diagnosed and treated early.
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Living with a noncancerous blood disorder can be exhausting. But there’s hope. Cleveland Clinic’s benign hematology experts provide personalized care and support.
Last reviewed on 06/19/2025.
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