The Bence Jones protein is an antibody fragment (called a kappa or lambda light chain) not normally found in the urine. This protein is not detected during routine urinalysis screening for urine proteins. The presence of the Bence Jones protein is often suspected based on abnormalities in the electrophoresis of blood proteins. Bence Jones protein screening is always combined with a total urine protein test. This test can be done on a single urine sample or on a 24-hour urine collection.
The presence of Bence Jones proteins may indicate excess light chain production of a single type of antibody (monoclonal production) by the bone marrow cells (plasmocytes). This overproduction can be either without immediate clinical significance (MGUS or monoclonal gammopathy of undetermined significance) or from multiple myeloma, a type of bone marrow cancer. If the test is positive, a comment indicates the nature of the light chain present (kappa or lambda). Bence Jones proteins can also be found in certain benign conditions.