Bence Jones proteins are the "light chain" portion of immunoglobulin protein excreted in the urine of myeloma patients.
The presence of protein is a sign that there are higher than normal levels of protein in the blood, as in the case of myeloma where there is an over production of immunoglobulin protein. When Bence Jones proteins are in the urine, they can accumulate and cause kidney damage.
This abnormal protein is usually detected with a 24 hour urine collection. Bence Jones proteins are named for Henry Bence Jones, a chemical pathologist who first discovered the unusual properties of these urine samples in the mid-1800s.