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Key Features

  • Monoclonal immunoglobulin (ie, paraprotein) in the serum (< 3 g/dL {< 30 g/L}) or urine

  • Clonal plasma cells in the bone marrow < 10% (if performed)

  • No symptoms and no organ damage from the paraprotein

  • MGUS is present in 1% of all adults

    • 3% of those over age 50 years

    • > 5% of those over age 70 years

  • Among all patients with paraproteins, MGUS is far more common than plasma cell myeloma

Clinical Findings

  • Defined as bone marrow monoclonal plasma cells < 10% in the setting of a paraprotein (serum M-protein < 3 g/dL [30 g/L]) and the absence of plasma cell–related end-organ damage

  • If an excess of serum free light chains (kappa or lambda) is established, the kappa to lambda ratio is 100 or less or 0.01 or greater

  • In approximately one-quarter of cases, MGUS progresses to overt malignant disease in a median of one decade

  • The transformation of MGUS to plasma cell myeloma is ~ 1% per year

  • Twelve percent of patients with MGUS will convert to amyloidosis in a median of 9 years

  • Plasma cell myeloma, smoldering plasma cell myeloma, and MGUS must be distinguished from reactive (benign) polyclonal hypergammaglobulinemia (which is commonly seen in cirrhosis or chronic inflammation)

Laboratory Findings

  • To establish the diagnosis,

    • Serum or urine, or both, should be sent for protein electrophoresis (PEP) and immunofixation electrophoresis (IFE) to search for a monoclonal protein

    • Serum should be sent for free light chain analysis and quantitative immunoglobulins

  • Additional tests include a hemoglobin and serum albumin, calcium, and creatinine

  • If these additional tests are normal (or if abnormal but are otherwise explained), then a bone marrow biopsy is usually deferred provided the serum M-protein is < 3 g/dL (< 30 g/L)

  • Radiographs are obtained in asymptomatic individuals

  • MRI or PET-CT imaging is preferred there are some bone complaints or a question regarding bone disease

  • MGUS is diagnosed if patients do not meet the criteria for smoldering plasma cell myeloma or plasma cell myeloma


  • None; patients are observed

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