High Quality Content by WIKIPEDIA articles! A paraprotein is an immunoglobulin or immunoglobulin light-chain that is produced in excess by the clonal proliferation of plasma cells. Detection of paraproteins in the urine or blood is 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. Paraproteins form a narrow band, or `spike` in protein electrophoresis as they are all exactly the same protein.