Key differentiating features of multiple myeloma, smoldering multiple myeloma, and monoclonal gammopathy of undetermined significance

	MGUS	SMM	MM
Clonal BM plasma cells	<10%	10 to 59% and/or Either serum ≥30 g/L or Urine ≥500 mg/24 hours	≥10% or biopsy proven plasmacytoma
M protein	Serum <30 g/L Urine <500 mg/24 hours		Any level
Myeloma-defining events (CRAB SLiM criteria)*	None	None	Present

The table illustrates key differentiating features of MGUS, SMM, and MM. Refer to UpToDate topics for a description of the full diagnostic criteria.

MGUS: monoclonal gammopathy of undetermined significance; SMM: smoldering multiple myeloma; MM: multiple myeloma; BM: bone marrow; CT: computed tomography; PET: positron emission tomography.
* These acronyms represent the following markers of MM-related organ/tissue impairment (CRAB) and biomarkers associated with near inevitable progression to end-organ damage (SLiM):

C: Hypercalcemia: serum calcium >0.25 mmol/L (>1 mg/dL) higher than the upper limit of normal or >2.75 mmol/L (>11 mg/dL)
R: Renal insufficiency: creatinine clearance <40 mL per min or serum creatinine >177 micromol/L (>2 mg/dL)
A: Anemia: hemoglobin value of >20 g/L below the lower limit of normal, or a hemoglobin value <100 g/L
B: Bone lesions: one or more osteolytic lesions on skeletal radiography, CT, or PET/CT
S: ≥60% clonal plasma cells in the bone marrow
Li: Involved/uninvolved serum free light chain ratio ≥100
M: MRI with >1 focal lesion involving bone or bone marrow

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Key differentiating features of multiple myeloma, smoldering multiple myeloma, and monoclonal gammopathy of undetermined significance