Monoclonal gammopathy of undetermined significance (MGUS) is an abnormal finding of a blood test. It means there’s a specific protein present in your blood and is an early sign of certain types of a cancer called myeloma.

Monoclonal gammopathy of undetermined significance (MGUS) is the name for a laboratory finding of an abnormal protein in the blood. This condition needs to be monitored because sometimes it is an early sign of developing smoldering myeloma or multiple myeloma, which are types of cancer.

The protein (called monoclonal protein, or M protein) is made by white blood cells called plasma cells in your body’s bone marrow. “Monoclonal“ means that there’s only one type of this abnormal protein.

MGUS isn‘t always a cause for concern and may not cause adverse health effects. But by the nature of its significance being undetermined, doctors have to watch it to find out.

Sometimes, healthy cells in the bone marrow can get crowded out by dividing plasma cells, which may cause an elevated M protein. Tissue damage is caused by high levels of M protein being deposited in the tissue.

Doctors often recommend monitoring people with MGUS by performing regular blood tests to check for any signs of cancer or disease that may develop over time.

MGUS usually doesn‘t lead to any symptoms of illness. Many doctors find M protein in the blood of people with MGUS while testing for other conditions. Some people may have symptoms like:

  • a rash
  • numbness
  • tingling in the body

The presence of M proteins in the urine or blood is the defining feature of MGUS. Other proteins may also be elevated in the blood when a person has MGUS, but they can also be signs of other health conditions such as dehydration or hepatitis.

To rule out other conditions or to see if MGUS is causing your health problems, a doctor may run other tests. These tests include:

  • Detailed blood tests. Some examples include a complete blood count, a serum creatinine test, and a serum calcium test. These tests can help check for signs of MGUS-related conditions such as an imbalance of blood cells, high calcium levels, and decreased kidney function.
  • A 24-hour urine protein test. This test can see if M protein is released in your urine and check for kidney damage, which could be a sign of a serious MGUS-related condition.
  • Imaging tests. A CT scan or MRI can check for bone abnormalities associated with serious MGUS-related conditions.
  • A bone marrow biopsy. A doctor uses this procedure to check for signs of bone marrow cancers and diseases associated with MGUS. A biopsy is usually only done if you show signs of the disease, such as unexplained anemia, kidney failure, bone lesions, or high calcium levels.

Doctors and scientists aren‘t sure exactly what causes MGUS. It’s thought that certain genetic changes and environmental factors may affect whether a person develops this condition.

What doctors do know is that MGUS causes abnormal plasma cells in the bone marrow to produce M protein.

The prevalence of MGUS is twice as high in African Americans when compared with white Americans. This is most likely be due to genetic factors. Environmental factors are possible, but evidence is lacking. Other risk factors include:

  • older age
  • being male
  • having a family history of MGUS or related diseases
  • having chronic infections or chronic inflammatory conditions
  • smoking

About 3.2 percent of people over age 50 and about 5.3 percent of people over age 70 have MGUS. Many of these people never end up having health issues related to MGUS.

Each year, the risk of MGUS progressing to multiple myeloma is about 1 percent. MGUS can also progress to other types of blood disorders. The type of conditions that can develop depend on which type of MGUS you have.

There are three types of MGUS, each associated with an elevated risk of certain health conditions. These types include:

  • Non-IgM MGUS (includes IgG, IgA, or IgD MGUS). This type affects the highest number of people with MGUS. There’s an increased chance that non-IgM MGUS will develop into multiple myeloma. In some people, non-IgM MGUS may lead to other serious disorders, such as immunoglobulin light chain (AL) amyloidosis or light chain deposition disease.
  • IgM MGUS. This type affects about 15 percent of those with MGUS. It comes with the risk of developing a rare cancer called Waldenstrom‘s disease, as well as lymphoma, AL amyloidosis, and multiple myeloma.
  • Light chain MGUS (LC-MGUS). This type causes M proteins to be detected in the urine, and it can lead to light chain multiple myeloma, AL amyloidosis, or light chain deposition disease.

The diseases triggered by MGUS may cause bone fractures, blood clots, and kidney problems over time. These complications can make managing the condition and treating any associated diseases more challenging.

There’s no way to treat MGUS. It doesn‘t go away on its own, but it doesn‘t usually cause symptoms or develop into a serious condition.

A doctor will recommend regular checkups and blood tests to keep an eye on your health. Usually, these checkups start 6 months after first diagnosing MGUS.

Besides checking the blood for changes in M proteins, your doctor will look for certain symptoms that could indicate the disease is advancing. These symptoms include:

Because MGUS can lead to conditions that deteriorate bone mass, a doctor may recommend that you take medication to increase your bone density if you have osteoporosis. Some of these medications include:

Researchers are continuing to improve their understanding of MGUS. The U.S. National Library of Medicine currently lists more than 100 clinical trials examining MGUS. In current trials, researchers are:

  • examining blood samples to improve their understanding of the cause of MGUS
  • collecting blood samples to collect data about the prevalence of MGUS in certain populations
  • examining the risk of MGUS progressing to multiple myeloma and other blood disorders in people with close relatives with MGUS
  • examining genetic markers associated with a genetic predisposition of MGUS
  • examining if daratumumab can treat certain kidney diseases

Most people with MGUS don’t develop serious blood and bone marrow conditions. However, regular doctor visits and blood tests can help estimate your risk. Your doctor can also determine your risk of MGUS progressing into another disease by taking into account:

  • The count, type, and size of M proteins found in your blood. Larger and more numerous M proteins may indicate a developing disease.
  • The level of free light chains (another kind of protein) in your blood. Higher levels of free light chains are another sign of developing disease.
  • The age at which you were diagnosed. The longer you’ve had MGUS, the higher your risk of developing a serious disease.

If you or a loved one is diagnosed with MGUS, be sure to follow your doctor’s plans for monitoring your condition.

Here are the answers to some of the common questions people have about MGUS:

Is MGUS a form of cancer?

MGUS is a precancerous condition. Precancerous means that it’s not cancer, but it has the potential to progress to cancer. Some people with MGUS go on to develop multiple myeloma or other blood cancers, but the majority do not.

Does MGUS always turn into myeloma?

Each year, MGUS has about a 1 percent chance of progressing into multiple myeloma. In a large study, researchers indicated the chances of MGUS becoming multiple myeloma over a 35-year period were:

Years after diagnosisChances of progression
1010%
2018%
3028%
3536%

Can you live a long life with MGUS?

Many people don’t experience any problems from MGUS, and many go on to live full lives.

MGUS is rare in people under age 40, and the majority of people with MGUS don’t develop multiple myeloma even 35 years after their diagnosis.

Is MGUS an autoimmune disease?

MGUS isn’t an autoimmune disease, but it may be provoked by autoimmune diseases. Research from 2014 suggests that people with autoimmune diseases have a 42 percent increased risk of developing MGUS.

Autoimmune conditions linked to MGUS include:

Does it run in families?

Studies indicate that people with a first-degree relative with MGUS or multiple myeloma have a 2 to 3 times higher risk of developing MGUS. A first-degree relative is a full sibling or biological parent.

Studies have also found that a family history of multiple myeloma is associated with a 2 to 4 times increased risk of developing multiple myeloma.

MGUS is a lab finding that may progress into some cancerous conditions. It should be monitored with the help of a physician.

Staying on top of your MGUS with regular checkups and blood tests can minimize your risk of complications. It can also increase your chances of a more positive outcome should you develop any MGUS-related disease.

Maintaining a health-promoting lifestyle can also lead to better outcomes. You can do this by getting enough sleep and exercise, reducing stress, and eating nutritious foods such as fresh fruits and vegetables.