What Is a Bence-Jones Protein Test?

Medically Reviewed by Melinda Ratini, MS, DO on February 29, 2024
4 min read

A Bence-Jones protein test is a urine test that looks for unusual levels of this protein. Other names for this test include urine immunofixation electrophoresis and an immunoassay for free light chains.  

Your doctor might recommend this test if you have: 

  • Many infections
  • High levels of blood calcium
  • Low levels of platelets
  • Low levels of red and white blood cells
  • A diagnosed multiple myeloma — a type of cancer  

The Bence-Jones protein is a kind of light chain protein that’s found in some of your antibodies. Antibodies are a type of molecule made by your immune system that are tailored to fight particular kinds of infection. 

When specific types of damage happen to your immune system — including some cancers and rare diseases — your body stops making unique antibodies to fight off infections. Instead, you begin to make monoclonal antibodies, which are all one kind and cannot help you fight off diverse infections. Bence-Jones proteins are part of one monoclonal antibody. 

These proteins are very small and not normally detectable in your urine, but when there are large amounts of them in your blood, they get filtered through your kidneys and into your urine. Filtering Bence-Jones proteins can damage your kidney and cause inflammation and obstruction of kidney cells. 

The protein was first described in 1845 and was given the name Bence-Jones in 1880. Finding Bence-Jones proteins in your urine is a sign of a serious underlying medical problem. 

The normal amount of Bence-Jones proteins in your urine is none at all. If you have detectable levels of this protein in your urine, then it’s usually a sign of a particular cancer or other condition. 

The exact level of the protein found in the test will vary based on your age, gender, health history, and the particular method of detection that your medical provider uses. 

In general, your test results are considered negative — normal — when your medical team doesn’t find any of these proteins in your urine, and the results are positive when they do.  

The main cause of abnormal Bence-Jones protein levels in your urine is a type of cancer called multiple myeloma. This cancer affects your blood cells and forms tumors inside your bones. This eventually starts to disrupt your antibody production and leads to high levels of free Bence-Jones protein. 

Approximately 50% to 80% of all people with multiple myeloma have Bence-Jones proteins in their urine. 

Other — less common — causes of high urine Bence-Jones protein levels include: 

  • Amyloidosis. This is an abnormal build-up of proteins in your tissues.
  • Lymphomas. This is a type of cancer that affects your lymphatic system — which is the largest part of your immune system.  
  • Waldenstrom macroglobulinemiaThis is a rare kind of cancer — a type of non-Hodgkin Lymphoma
  • Monoclonal Gammopathy of Undetermined Significance (MGUS). With this condition, your plasma cells make more of one type of antibody than they should. It doesn’t result in tumors and usually doesn’t need treatment when it’s your only condition. 

If you’ve already been diagnosed with multiple myeloma, then the test may be used — at the same time as other tests — as a Bence-Jones protein symptom checker. This would help your doctor tell how far along your cancer has progressed.    

The first step of a Bence-Jones protein test is to collect a urine sample. The exact type of sample that you collect will depend on which testing method your medical team plans on using. 

One method is a 24-hour collection that you’ll do at home. For this test, you completely empty your bladder in the morning without collecting a sample. Then, you collect urine in a provided container every time you urinate for the next 24 hours. 

More often, you’ll just need to provide a single urine sample while you’re in the office. 

All of your urine samples need to be clean-catch samples, which means that you don’t want to get any germs from your penis or vagina in with the urine. Your doctor may provide a kit to help make sure this doesn’t happen. This will include sterile wipes and specific instructions for the sample collection.  

Once your medical team has your sample there are a number of different methods that they can use to analyze the levels of Bence-Jones protein. These include:

  • Strips. Some strips can change color in the presence of this protein. This is the worst method of protein detection. 
  • Urine immunofixation electrophoresis. This is a way of spreading all of the proteins in your urine out in a gel, then testing them for the presence and quantity of this particular protein. It’s the most common method.
  • Free light chain assay. This is the newest method of Bence-Jones protein analysis. It compares the relative amounts of Bence-Jones protein to the total amount of all light chain proteins in your urine.