The first test for recognition of monoclonal gammopathies should be serum protein electrophoresis with high-resolution agarose gel. Serum protein electrophoresis should be performed whenever multiple myeloma, Waldenström's macroglobulinemia, primary amyloidosis, or a related disorder is suspected. Immunofixation is critical for the differentiation of a monoclonal from a polyclonal increase in immunoglobulins. Quantitation of immunoglobulins should be performed with a rate nephelometer. The viscosity of serum should be measured if the patient has signs or symptoms of hyperviscosity syndrome. A 24-hour urine specimen should be obtained for determination of the total amount of protein excreted each day. Immunofixation of the urine should be performed on every patient who has an M-protein level greater than 1.5 g/dL (15 g/L) in the serum or in whom multiple myeloma, Waldenström's macroglobulinemia, primary amyloidosis, or a related disorder is suspected.