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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Monoclonal gammopathy of undetermined significance

Haematology and transfusion · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull
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Paraprotein with acute organ injury

New renal failure, hypercalcaemia, cord symptoms, hyperviscosity, severe neuropathy, haemolysis, nephrotic syndrome or heart failure is not uncomplicated MGUS and requires urgent reclassification.

Action: Assess ABCDE, obtain FBC, calcium, renal, liver, SPEP, immunofixation, free light chains, urine and organ-specific tests, treat the acute syndrome and refer urgently to haematology, renal, neurology or cardiology for marrow, tissue and imaging rather than waiting for routine MGUS review.

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.
  • Initial tests are FBC, calcium, renal, liver, SPEP, immunofixation, quantitative immunoglobulins, free light chains and urinalysis or protein quantification plus symptom and examination review.
  • Do not perform routine marrow or whole-body imaging in every clearly low-risk asymptomatic IgG MGUS case, but investigate unexplained red flags, higher burden, IgM or light-chain disease appropriately.
  • Common progression risk factors are non-IgG isotype, M-protein at least 15 g/L and abnormal free-light-chain ratio; risk category guides follow-up intensity.
  • A stable low-risk patient may be returned to primary care or discharged with explicit blood-test and symptom triggers under the BSH pathway; higher-risk disease needs structured haematology follow-up.
  • MGUS itself is not treated with chemotherapy; treat osteoporosis, infection and cardiovascular risks conventionally and treat a demonstrable monoclonal protein-mediated disorder through its specialist pathway.
  • A small clone does not mean harmless protein: renal biopsy, nerve assessment or Congo-red tissue may reveal monoclonal gammopathy of clinical significance or AL amyloid.
  • Do not screen the general population and do not repeatedly test a paraprotein without explaining the purpose, interval and action threshold.

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.

Proteinuria, oedema, restrictive cardiomyopathy, autonomic neuropathy, macroglossia or periorbital bruising suggests AL amyloidosis and needs urgent tissue typing.

Headache, visual disturbance, mucosal bleeding or neurological symptoms with an IgM paraprotein suggests hyperviscosity and cannot wait for routine surveillance.

A rapidly rising M-protein, markedly changing free-light-chain ratio, constitutional symptoms, nodes or spleen requires lymphoma or plasma-cell re-evaluation.

Investigation priorities

01
First-line monoclonal studiesFirst stepFirst line

Confirm isotype, concentration and light-chain clonality.

Management branches

New monoclonal proteinConfirm clone and search for consequence

SPEP, immunofixation or free-light-chain testing detects possible monoclonality.

  1. Repeat or complete isotype, concentration, immunoglobulin and free-light-chain characterisation with FBC, renal, calcium, urine and symptom assessment.
  2. Escalate marrow, whole-body imaging, CT or tissue biopsy when burden, isotype, dynamic change or organ features warrant.
  3. Classify non-IgM, IgM or light-chain MGUS only after excluding active malignancy, amyloid and monoclonal gammopathy of clinical significance.
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Sources and review status3 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • British Society for Haematology MGUS good practice paperCurrent UK diagnosis, risk, monitoring and MGCS guidance.
  • NICE NG35 myeloma recommendationsUK paraprotein testing, imaging and active-myeloma exclusion.
  • British Society for Haematology early AL amyloidosis guidelineCurrent 2026 red flags for a small amyloidogenic clone.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom