High protein in urine or blood: What M protein and MGUS actually mean
Fact-checked by M protein is an abnormal antibody that’s produced in certain diseases, including the blood cancer multiple myeloma and the noncancerous condition monoclonal gammopathy of undetermined significance (MGUS), that affect plasma cells.
Monitoring the type and levels of M protein helps doctors make a diagnosis, track disease progression, and estimate the risk of MGUS progression to myeloma. Knowing the meaning of M protein test results will help individuals understand their own risk and outlook.
What is M protein and why measure it?
Plasma cells are antibody-producing immune cells that are generated in the bone marrow. The antibodies they make help protect the body against illness. Normally, plasma cells and their antibodies have some genetic variability, which helps them effectively fight off different types of invaders.
In multiple myeloma and related plasma cell disorders, an abnormal plasma cell grows out of control and produces many genetically identical clones of itself. These cells then overproduce a group of genetically identical, abnormal antibodies called monoclonal protein, or M protein.
M protein does not function as a normal antibody should, and can cause serious problems in the bone marrow and other tissues. It may also be called myeloma protein or paraprotein.
Doctors measure M protein to identify and monitor the progression of plasma cell disorders such as multiple myeloma, MGUS, Waldenström’s macroglobulinemia, and light chain amyloidosis.
High protein in blood or urine
Standard blood tests measure total protein levels. If M protein is present, total protein levels will rise, but many other factors, serious or not, can cause that test result. High protein in blood may prompt doctors to order more specific tests to measure antibody levels and monoclonal protein specifically. Likewise, high protein in the urine could be due to elevated M protein.
M protein can be detected in blood and urine by a lab test called electrophoresis. It is not produced in a healthy body, so its presence is considered abnormal and may indicate a plasma cell disorder. However, this does not always mean that a person has cancer.
There are also several types of M protein, and some are more closely linked to specific conditions. For example, immunoglobulin G (IgG) is the most common type associated with multiple myeloma.
Ultimately, the amount and type of M protein present can give doctors a clue as to which specific condition a person has. It can also help determine its subtype and how likely it is to progress.
How MGUS differs from myeloma
MGUS is a precancerous blood disorder that is considered a risk factor for the development of myeloma. It progresses to myeloma or another serious blood condition in about 20%-25% of people.
The condition is characterized by a small number of M protein-producing plasma cells in the bone marrow that haven’t caused significant myeloma-defining damage. In contrast, many more abnormal plasma cells are produced in myeloma, leading to serious bone marrow problems and organ damage.
MGUS is defined by M protein levels below 3 grams per deciliter (g/dL), without any myeloma symptoms. If M protein levels exceed this threshold, a person may be considered to have either the precancerous condition smoldering myeloma or active multiple myeloma, depending on whether myeloma symptoms are present.
Higher M protein levels or certain M protein types may be associated with a higher risk of MGUS progressing to myeloma.
Follow-up tests
If M protein levels are slightly elevated and there are no clinical symptoms, an individual will likely be diagnosed with MGUS. The person will need regular blood and urine tests to monitor changes in M protein levels, with the frequency determined by the individual’s risk of progression to myeloma.
The MGUS test results will inform what needs to happen next, but many people will need MGUS monitoring without intervention for many years.
If M protein levels are more elevated or signs and symptoms are present, doctors may order bone marrow biopsies or imaging tests to identify possible signs of blood cancer.
Questions to ask
When an M protein test comes back positive, there are a few questions patients can ask to better understand their situation:
- What type of M protein do I have, and how much is present?
- Do I have MGUS, smoldering myeloma, active myeloma, or another blood disorder?
- What types of follow-up tests do I need to confirm my diagnosis?
- What is my risk of progression to cancer, and how often do I need to get checked?
- Do I need to make any lifestyle changes or start any treatments?
- What are some symptoms I should look out for?
Asking these questions will help individuals best understand what their M protein test result means for them now and in the future.
Rare Cancer News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
