CRAB / SLiM-CRAB Criteria

IMWG myeloma-defining events for the diagnosis of multiple myeloma
Clonal bone-marrow plasma cells
Biopsy-proven bony or extramedullary plasmacytoma
Myeloma-defining events (CRAB and SLiM biomarkers)
C — hypercalcaemia: serum calcium > 0.25 mmol/L (> 1 mg/dL) above the ULN, or > 2.75 mmol/L (> 11 mg/dL)
R — renal insufficiency: creatinine clearance < 40 mL/min, or serum creatinine > 177 µmol/L (> 2 mg/dL)
A — anaemia: haemoglobin > 20 g/L below the LLN, or < 100 g/L (< 10 g/dL)
B — ≥ 1 osteolytic lesion on skeletal radiography, CT, or PET-CT
Involved : uninvolved serum free light-chain ratio ≥ 100 (involved iFLC ≥ 100 mg/L)
> 1 focal lesion ≥ 5 mm on MRI
Evidence
Original publication
Rajkumar SV, Dimopoulos MA, Palumbo A, et al. International Myeloma Working Group updated criteria for the diagnosis of multiple myeloma. Retained the CRAB features and added three biomarkers of malignancy (clonal bone-marrow plasma cells ≥ 60%, involved:uninvolved serum free light-chain ratio ≥ 100, and > 1 focal lesion on MRI) that also define myeloma requiring therapy.
Lancet Oncology, 2014
Open source
Guideline
Applied when clonal bone-marrow plasma cells are ≥ 10% or a plasmacytoma is biopsy-proven. Smouldering myeloma additionally requires a serum M-protein ≥ 30 g/L, urinary M-protein ≥ 500 mg/24 h, or 10–60% clonal plasma cells, with no myeloma-defining event and no amyloidosis.
Last reviewed: 2026-09
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