Myeloma and macroglobulinemia: what are the criteria for diagnosis?

Monoclonal gammopathy of undetermined significance (MGUS) is much more common than either multiple myeloma or Waldenström's macroglobulinemia. Since individuals with MGUS do not need treatment but only monitoring, it is important to distinguish this group from those with progressive plasma cell disorders. Criteria for diagnosis of myeloma and macroglobulinemia and laboratory pitfalls related to meeting these criteria are discussed. The importance of using the serum protein electrophoretic pattern in determining the magnitude of the monoclonal immunoglobulin component and the need for accurate quantification and characterization of urine protein are emphasized. Uniform definitions and consensus on diagnostic standards are becoming increasingly necessary if more effective and less toxic therapeutic approaches for patients with myeloma and macroglobulinemia are to be applied in an optimal manner.