MGUS and the new paraprotein workup: the AU general practice approach

A single abnormal band on serum protein electrophoresis is one of the more common unexpected laboratory findings in Australian general practice. Roughly 3% of Australians over 50 and 5% over 70 have MGUS — monoclonal gammopathy of undetermined significance — most without any symptoms and most discovered incidentally. The term sounds alarming but is deliberately chosen to reflect exactly what it is: a clonal plasma-cell abnormality with uncertain long-term significance at the time of detection.

The GP’s role is threefold: complete a systematic workup that characterises the protein and excludes organ damage; apply a validated risk score to stratify progression likelihood; and establish a surveillance plan that detects progression without over-medicalising a benign finding in most patients.

A. Core clinical — the AU general-practice framework

What MGUS is — and what it is not

Per Therapeutic Guidelines haematology and the IMWG 2014 criteria, MGUS is defined by:

• Serum paraprotein less than 30 g/L
• Bone-marrow clonal plasma cells less than 10%
• No CRAB features and no myeloma-defining events

CRAB stands for: Calcium elevation (corrected serum calcium >2.75 mmol/L), Renal impairment (eGFR <40 or creatinine >177 attributable to the clone), Anaemia (haemoglobin <100 g/L or >20 g/L below baseline), Bone lesions (≥1 lytic lesion on imaging).

Smouldering myeloma sits between MGUS and active myeloma: paraprotein ≥30 g/L or bone-marrow plasma cells 10–60%, but still no CRAB features. Active multiple myeloma requires ≥10% clonal plasma cells plus CRAB features or a myeloma-defining event (plasma cells ≥60%, serum free light-chain ratio ≥100 with the involved chain ≥100 mg/L, or ≥1 focal MRI lesion ≥5 mm on whole-body imaging).

What triggers a paraprotein workup in general practice

Myeloma Australia guidelines list the common presentations prompting investigation:

• Unexplained anaemia, especially with a high ESR or rouleaux on the blood film
• Bone pain or an unexpected fracture or vertebral compression
• Hypercalcaemia identified incidentally or symptomatically
• Unexplained renal impairment, particularly if proteinuria is also present
• Recurrent bacterial infections suggesting reduced immunoglobulin levels
• Peripheral neuropathy — painful, length-dependent
• Carpal tunnel, macroglossia, or periorbital bruising — classic AL amyloidosis features
• Unexplained cardiac thickening or heart failure with low ECG voltages
• Incidental SPEP finding on a test ordered for another reason

The comprehensive new-paraprotein workup

Per the RCPA Manual and HSANZ position statement, a complete workup includes:

Characterise the paraprotein:

• SPEP — serum protein electrophoresis: quantifies the M-band in g/L and identifies the gamma-region spike
• Serum immunofixation (SIFE) — confirms monoclonality and identifies the heavy chain (IgG, IgA, IgM) and light chain (κ or λ)
• Serum free light chains (Freelite assay) — measures κ and λ free light chains; the κ:λ ratio (normal 0.26–1.65; up to 3.10 acceptable in chronic kidney disease) is a key prognostic input
• Quantitative immunoglobulins — IgG, IgA, and IgM to assess immunoparesis
• Urine Bence Jones / 24-hour urine protein electrophoresis with immunofixation — detects free light-chain (Bence Jones) proteinuria

Assess for CRAB organ damage:

• FBC with film; U&E and eGFR; corrected calcium; albumin; LDH; β2-microglobulin
• Urine ACR or PCR for proteinuria

Imaging:

• The IMWG 2019 imaging consensus recommends whole-body low-dose CT (WBLDCT) as first-line — superior sensitivity to the older skeletal survey for detecting lytic lesions
• Whole-body MRI when WBLDCT is non-diagnostic, for soft-tissue plasmacytoma, or to detect MDE-qualifying focal marrow lesions ≥5 mm
• Skeletal survey is now considered inadequate as the sole imaging study in 2026

Mayo Clinic risk stratification

The Mayo three-factor risk score (Rajkumar Blood 2005) uses three variables, each scoring one point:

1. Non-IgG isotype (IgA, IgM, or biclonal)
2. Paraprotein ≥15 g/L
3. Abnormal serum free light-chain ratio (κ:λ <0.26 or >1.65)

Risk group	Factors	20-year cumulative progression
Low	0	~5%
Low-intermediate	1	~21%
High-intermediate	2	~37%
High	3	~58%

Surveillance after the initial workup

Per HSANZ and Myeloma Australia:

• Low-risk MGUS (0 factors, no organ involvement): repeat workup at 6 months to confirm stability, then every 2–3 years while asymptomatic
• Intermediate-risk (1–2 factors): 6-monthly initially, then annually; specialist input appropriate
• High-risk MGUS (3 factors): 3–6 months for the first 2 years, then annually; specialist co-management strongly advised
• Smouldering myeloma: 3-monthly review; specialist care; clinical trial consideration

Surveillance bloods include FBC, U&E, corrected calcium, SPEP, SIFE, SFLC, and quantitative immunoglobulins. New CRAB symptoms or signs at any time — bone pain, infection, swelling, frothy urine, unexplained fatigue — prompt urgent re-evaluation including imaging and bone-marrow assessment rather than waiting for the scheduled review.

B. Evidence — risk stratification, imaging, and the treatment threshold

The Kyle Olmsted cohort (NEJM 2018) provides the foundational long-term data: annual progression of approximately 1% per year to myeloma, amyloidosis, or a related disorder, with a risk that does not plateau even after stable years. This finding underpins the recommendation to continue surveillance indefinitely in all risk groups rather than discharging after a period of stability.

Why not treat low-risk MGUS? Multiple studies have failed to show a survival benefit from treating the underlying plasma-cell clone in MGUS, while the therapies themselves (corticosteroids, chemotherapy, immunotherapy) carry meaningful toxicity. The standard of care remains watchful waiting.

High-risk smouldering myeloma is an active area of clinical trial activity. The QuiRedex trial (Mateos NEJM 2013) and CENTAURUS trial (daratumumab) suggested that treating high-risk smouldering myeloma before CRAB features emerge may delay progression, but this remains investigational rather than standard Australian practice outside of clinical trials.

The case for whole-body low-dose CT is strong — the IMWG 2019 consensus demonstrated that skeletal survey misses 20–40% of lytic lesions detectable on WBLDCT. The practical consequence is that WBLDCT is now the imaging standard for the initial new-paraprotein workup, shifting the diagnosis of some patients from MGUS to smouldering or active myeloma.

C. AL amyloidosis — recognising it before organs fail

AL amyloidosis develops when monoclonal free light chains deposit in organs and disrupt function. It is the most dangerous MGUS-related complication and can occur even with small paraprotein levels. Per eTG, the classic organ presentations are:

Organ	Cardinal clues
Heart	Concentric LV thickening on echo, low ECG voltages, elevated NT-proBNP, unexplained heart failure
Kidney	Nephrotic-range proteinuria with bland urinary sediment
Peripheral nerves	Painful length-dependent sensorimotor neuropathy, carpal tunnel
Autonomic nervous system	Orthostatic hypotension, gastroparesis, bowel dysmotility
Liver	Hepatomegaly, elevated alkaline phosphatase
Skin and soft tissue	Periorbital bruising (“raccoon eyes”), waxy skin, macroglossia

Diagnosis requires tissue biopsy — typically abdominal fat aspirate or affected-organ biopsy — with Congo-red staining and mass spectrometry for amyloid typing. Specialist amyloidosis centres in Australia include the Princess Alexandra Hospital Brisbane, Royal Melbourne Hospital, and Royal North Shore Sydney.

Treatment targets the underlying plasma-cell clone (usually with daratumumab-based regimens at specialist centres) to stop further light-chain production; organ function often stabilises but rarely fully reverses. Early recognition dramatically improves outcomes — amyloidosis diagnosed at the cardiac failure stage carries a median survival of less than 2 years without treatment.

D. Australian operations

Referral to haematology is indicated for:

• Any CRAB feature at any point
• Paraprotein ≥15 g/L (Mayo intermediate or high risk)
• IgM paraprotein with neuropathy, hyperviscosity symptoms, or organomegaly
• Any suspicion of AL amyloidosis
• Abnormal SFLC ratio outside CKD adjustment
• Smoldering myeloma confirmed on imaging or bone-marrow assessment
• Significant immunoparesis with recurrent infections
• Patient preference for specialist co-management

MBS items supporting the paraprotein workup:

• SPEP: MBS item 66524; SIFE: 66525; SFLC Freelite: 66527; quantitative immunoglobulins: 66520
• FBC: 65070; U&E, calcium: 66506 and 66602; β2-microglobulin: 66510; LDH: 66821
• Whole-body low-dose CT: MBS 56226
• Bone-marrow aspirate and trephine: item 30087 (haematologist)
• GP consultation: items 23, 36, and 44; chronic condition management plan (GPCCMP) from 1 July 2025: items 965 and 967

PBS-listed myeloma therapies (for reference — all initiated by haematologists via Authority prescription):

• Bortezomib (Velcade), lenalidomide (Revlimid), daratumumab (Darzalex SC): Authority Required for newly diagnosed and relapsed myeloma
• Zoledronic acid and denosumab (Xgeva): PBS Authority for myeloma bone disease

Patient support — Myeloma Australia provides patient-facing resources, a myeloma nurse service, and peer support groups. The Cancer Council Australia Optimal Cancer Care Pathway: Multiple Myeloma sets out endorsed timelines for referral and treatment.

E. Special populations

Older adults — MGUS prevalence rises steeply with age (7.5% over 85 in the Olmsted cohort), so it is a common incidental finding in aged care and general practice reviews. Surveillance intensity needs to be balanced with frailty and comorbidity; shared decision-making about the value of ongoing monitoring is appropriate in patients with limited life expectancy.

Aboriginal and Torres Strait Islander peoples — myeloma incidence is lower in First Nations populations but tends to present at more advanced stages. Unexplained anaemia, bone pain, or renal impairment warrants prompt investigation including SPEP. The 715 ATSI Health Assessment provides an appropriate entry point for comprehensive workup including pathology.

People with chronic kidney disease — the SFLC κ:λ ratio is elevated in CKD (acceptable up to 3.10 due to reduced renal clearance). Interpreting the ratio requires the CKD-adjusted reference range to avoid over-diagnosing light-chain MGUS.

Family members — first-degree relatives of myeloma patients have approximately double the background MGUS risk. Opportunistic SPEP testing at a general practice review is reasonable if they have relevant symptoms, but population screening is not recommended.

When to escalate

Return urgently or escalate to emergency if:

• New or severe bone pain, or a fracture on minimal trauma — potential pathological fracture
• Hypercalcaemia symptoms (polyuria, polydipsia, confusion, vomiting) — potential CRAB calcium event
• Acute kidney injury in a known MGUS patient — potential cast nephropathy or progression
• Hyperviscosity symptoms (visual change, headache, epistaxis, mucosal bleeding, neurological symptoms) — more common with IgM paraprotein; requires emergency plasmapheresis
• Any sign consistent with amyloidosis (cardiac, renal, neurological) in a patient with known paraprotein — urgent specialist referral for tissue diagnosis

What this article is and is not

This is general health information drawn from current Australian haematology guidelines — Therapeutic Guidelines, Myeloma Australia MSAG guidelines, HSANZ, Cancer Council Australia, and RCPA — and from landmark MGUS epidemiology and risk stratification studies. It does not constitute personal medical advice and does not create a doctor–patient relationship.

MGUS management depends on the specific paraprotein subtype, size, serum free light-chain ratio, and organ assessment. Decisions about surveillance frequency, referral timing, and if or when treatment is ever considered belong with your GP and haematologist.

For Australian patient-facing information: Myeloma Australia, HealthDirect, and Cancer Council Australia.

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Sources cited

1. Therapeutic Guidelines — Haematology (eTG complete)
2. Myeloma Australia — MSAG Clinical Practice Guidelines 2024
3. HSANZ — Haematology Society of Australia and New Zealand
4. Cancer Council Australia — Optimal Cancer Care Pathway: Multiple Myeloma 2024
5. RCPA Manual — Paraprotein investigation 2024
6. HealthDirect
7. Kyle RA et al. MGUS long-term follow-up (Olmsted cohort). NEJM 2018;378:241
8. Rajkumar SV et al. IMWG updated criteria. Lancet Oncol 2014;15:e538
9. Hillengass J et al. IMWG imaging consensus. Lancet Oncol 2019;20:e302
10. Rajkumar SV et al. Mayo risk stratification. Blood 2005;106:812
11. Mateos MV et al. QuiRedex trial. NEJM 2013;369:438