Synopsis
Confirm MGUS without missing myeloma, lymphoma, amyloid or monoclonal gammopathy of clinical significance, stratify progression risk and provide proportionate monitoring with clear re-referral triggers.
- MGUS is a diagnosis of exclusion: define the monoclonal isotype and burden, then show absence of a myeloma-defining event, lymphoma and protein-mediated organ disease.
- Non-IgM MGUS usually has serum M-protein below 30 g/L, clonal marrow plasma cells below 10% and no attributable SLiM-CRAB event.
- Light-chain MGUS has an abnormal free-light-chain ratio with raised involved light chain, no heavy-chain expression, marrow clonal plasma cells below 10% and urinary monoclonal protein below 500 mg/24 hours.
Key red flags
New bone pain, fracture, anaemia, hypercalcaemia, renal decline or recurrent infection raises active myeloma and requires repeat clonal and whole-body assessment.
Investigation priorities
Confirm isotype, concentration and light-chain clonality.
Management branches
SPEP, immunofixation or free-light-chain testing detects possible monoclonality.
- Repeat or complete isotype, concentration, immunoglobulin and free-light-chain characterisation with FBC, renal, calcium, urine and symptom assessment.
- Escalate marrow, whole-body imaging, CT or tissue biopsy when burden, isotype, dynamic change or organ features warrant.