What are considered myeloma defining events in the diagnosis of multiple myeloma (MM)?

Updated: Mar 06, 2020
  • Author: Dhaval Shah, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Myeloma-defining events include the following  [2] :

  • Serum calcium level >0.25 mmol/L (>1 mg/dL) higher than the upper limit of normal or >2.75 mmol/L (>11 mg/dL)
  • Renal insufficiency (creatinine >2 mg/dL [>177 μmol/L] or creatinine clearance < 40 mL/min)
  • Anemia (hemoglobin < 10 g/dL or hemoglobin >2 g/dL below the lower limit of normal)
  • One or more osteolytic bone lesions on skeletal radiography, CT, or PET-CT
  • Clonal bone marrow plasma cells ≥60%
  • Abnormal serum free light chain (FLC) ratio ≥100 (involved kappa) or < 0.01 (involved lambda)
  • One or more focal >5 mm lesions on MRI scans

In November 2014, the International Myeloma Working Group added the following criteria to the CRAB criteria for multiple myeloma [1] :

  • Bone marrow plasma cells (BMPCs) ≥60%
  • Involved/uninvolved serum free light chain ratio ≥100
  • Abnormal MRI with more than one focal lesion, with each lesion >5 mm

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