Paraprotein

A paraprotein is an abnormal protein in the urine or blood, most often associated with benign MGUS (monoclonal gammopathy of undetermined significance), where they remain "silent", and multiple myeloma. An excess in the blood is known as paraproteinemia.

These are immunoglobulins or immunoglobulin light-chains that are produced by the clonal proliferation of plasma cells. Paraproteins form a narrow band, or 'spike' in protein electrophoresis as they are all exactly the same protein.

Monoclonal free light chains in the serum or urine are called Bence Jones proteins.

History
The concept and term were introduced by the Berlin pathologist Dr Kurt Apitz in 1940, at that time the Oberarzt of the pathological institute at the Charité hospital.

Paraproteins allowed the detailed study of immunoglobulins, which eventually led to the production of monoclonal antibodies in 1975.