What to Know About Bence Jones Proteins

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Bence Jones proteins are small proteins produced by plasma cells—small enough to pass through your kidneys, one of your body's main filtration systems. When your body has too many of these proteins, they easily pass from your bloodstream into your urine. A person who has a type of cancer affecting the plasma cells, like multiple myeloma, often has Bence Jones proteins in their urine.

Bence Jones proteins are also referred to as M-proteins or light chains.


When a person has a blood disorder that affects plasma cells, it can cause plasma cells to proliferate uncontrollably and abnormally. It can also lead to only one type of cell becoming cloned. This results in an abundance of only one type of antibody protein, called a monoclonal antibody, or M-protein. Sometimes, these antibodies don't work as they should or are damaged or weak, and therefore unable to fight infection.

Light Chains

Light chains are monoclonal (M-proteins), meaning they come from just one type of cloned cell. The light chains formed by these cells are made up of many copies of the same small antibody parts. There are two types of light chains: kappa, and lambda. Each type will have a different effect on your body.

Conditions Marked by Bence Jones Proteins

Testing a person's urine to look for Bence Jones proteins can help healthcare providers diagnose several cancers of the lymphatic system, in addition to other conditions.

Multiple myeloma

Multiple myeloma is a type of blood cancer that begins in plasma cells (a kind of white blood cell). Plasma cells are found in your bone marrow and lymph nodes where they produce the antibodies your body needs to fight infections.

People with multiple myeloma are at a higher risk of infections, fractures, anemia, and bleeding problems. The cancer is incurable, but there are treatments—including stem cell transplantation in some cases. Between 50 and 80 percent of people with multiple myeloma will have a urine test positive for Bence Jones proteins.

Waldenstrom's macroglobulinemia

Waldenstrom's macroglobulinemia is an uncommon cancer occurring in B cells (a type of white blood cell). B cells go through a process to become antibody-producing plasma cells. In this disease, cancer occurs in the B cell before it has become a plasma cell. Waldenström’s macroglobulinemia is distinct from multiple myeloma, but both conditions can cause Bence Jones proteins in urine.

Monoclonal gammopathy of undetermined significance (MGUS)

MGUS is a condition that may be a precursor of multiple myeloma. It causes an increase in the number of plasma cells without the other symptoms associated with multiple myeloma.

Kidney disease

Ordinarily, antibodies are too large to be filtered through the tubules in the kidneys. Bence Jones proteins are small enough to enter the filtering units in the kidneys where they can build up and cause problems. Some types of proteins are more likely to harm the kidneys in this way than others.

Bence Jones Proteins Urine Test 

The urine test your healthcare provider will order to look for Bence Jones proteins is known by a few different names, including:

  • Urine protein electrophoresis (UPEP)
  • Urine immunofixation electrophoresis
  • Immunoassay for free light chains

Because the content of your urine changes throughout the day, you will need to collect all the urine you pass over the course of 24 hours. You will be given a container and instructions about collecting, storing, and transporting your sample to the lab.

Follow these instructions carefully to avoid contamination. The instructions may ask you to write down the time each time you pass urine during the 24-hour collection period. You may also need to record any medications you take or dietary supplements, as these can change the concentration of your urine.

If you have any questions or problems collecting your sample call your healthcare provider's office or the lab.

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By Abby Norman
Abby Norman is a freelance science writer and medical editor. She is also the author of "Ask Me About My Uterus: A Quest to Make Doctors Believe in Women's Pain."