01OverviewDefinition, clinical context and the essential points that orientate the chapter.
The term membranoproliferative glomerulonephritis describes how glomeruli respond to injury: mesangial hypercellularity and matrix expansion accompany thickened, double-contoured capillary walls. Modern classification begins with immunofluorescence. Immunoglobulin plus complement deposition usually indicates immune-complex formation; dominant C3 with scant immunoglobulin suggests dysregulation of the alternative complement pathway.
C3 glomerulopathy is subdivided into dense deposit disease, with highly electron-dense intramembranous deposits, and C3 glomerulonephritis, with less distinctive deposits. The renal pattern may coexist with acquired autoantibodies such as C3 nephritic factor, pathogenic variants in complement regulators, monoclonal proteins or infection triggers. A label therefore does not replace investigation of mechanism.
Treatment evidence is disease- and activity-dependent. Removing an infection or treating a pathogenic B-cell or plasma-cell clone may be decisive in immune-complex disease. For primary C3 glomerulopathy, supportive kidney care, expert pathology review, complement phenotyping and access to approved or commissioned therapy should be coordinated by a specialist centre. Recurrence after transplantation is common enough to influence counselling and donor planning.
Key points
- MPGN is a light-microscopic pattern of mesangial proliferation and capillary-wall remodelling, not a single aetiological diagnosis.
- Immunofluorescence separates immunoglobulin-associated immune-complex disease from C3-dominant glomerulopathy and directs the subsequent search.
- Immune-complex MPGN prompts evaluation for chronic infection, autoimmunity, cryoglobulinaemia and monoclonal gammopathy; genuinely idiopathic disease is uncommon.
- C3 glomerulopathy reflects alternative-complement-pathway dysregulation and comprises C3 glomerulonephritis and dense deposit disease, distinguished mainly by electron microscopy.
- Low serum C3 can support complement activation but may be normal, while reduced complement also occurs in immune-complex disease and is not diagnostic alone.
- Complement autoantibody, functional and genetic testing belongs in specialist laboratories and should follow careful phenotyping and exclusion of secondary drivers.
- Proteinuria control, blood-pressure management and cardiovascular protection remain important while disease-specific treatment is considered.
- New complement-directed therapies and their NHS status are evolving; use only current NICE, NHS England and expert-centre governance, never a historical web page as a prescription.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Chronic infection
Persistent microbial antigen from deep infection, endocarditis or chronic viral disease can drive circulating immune complexes and an MPGN pattern.
Autoimmune and cryoglobulin disease
Systemic autoimmunity and cryoglobulinaemia generate immunoglobulin-containing complexes that deposit in glomerular capillaries and activate complement pathways.
Monoclonal gammopathy
A small B-cell or plasma-cell clone may produce pathogenic monoclonal deposits or antibodies that perturb complement despite limited systemic tumour burden.
Alternative-complement dysregulation
Acquired complement autoantibodies or genetic pathway defects can sustain C3 activation, producing C3 glomerulonephritis or dense deposit disease.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Immune or complement deposition
Immunoglobulin-containing complexes or predominantly C3 fragments accumulate in mesangial and capillary-wall compartments throughout affected glomeruli during active disease.
- 2Mesangial and endothelial injury
Complement activation and inflammatory recruitment cause mesangial proliferation, endocapillary narrowing and leakage of blood and protein.
- 3Capillary-wall remodelling
Mesangial cells and matrix extend around deposits, creating duplication or double-contour appearances that define the membranoproliferative light-microscopy pattern.
- 4Progressive glomerular scarring
Uncontrolled driver activity produces sclerosis, tubular atrophy and interstitial fibrosis, converting active nephritic or nephrotic disease into chronic kidney impairment.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Haematuria, proteinuria, hypertension, oedema and reduced kidney function often coexist rather than forming a purely nephritic presentation.
Oliguria, accelerating creatinine, severe hypertension or fluid overload may reflect active proliferative injury and requires urgent nephrology assessment.
Fever, cardiac murmur, injected-drug exposure, indwelling infection or hepatitis risk should redirect evaluation before immunosuppression is contemplated.
Purpura, neuropathy, arthralgia, low complement and systemic symptoms suggest cryoglobulin-associated immune-complex disease requiring careful sample handling.
Partial lipodystrophy, retinal drusen, family clustering or recurrence after transplant supports specialist assessment for alternative-pathway dysregulation.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Kidney biopsy with light microscopy, immunofluorescence and electron microscopyFirst step - Why
- Define the MPGN pattern, dominant deposits, ultrastructure and chronic damage.
- Interpretation and limitations
- Immunoglobulin-rich staining favours immune-complex disease; C3-dominance raises C3 glomerulopathy, while dense ribbon-like deposits define dense deposit disease.
- 02
Urine microscopy and quantitative protein - Why
- Measure glomerular activity and establish a reproducible baseline.
- Interpretation and limitations
- Dysmorphic red cells or casts support glomerular bleeding; serial ACR or PCR and eGFR are more useful for response than a lone dipstick.
- 03
C3, C4 and specialist complement studies - Why
- Characterise complement consumption and investigate regulatory dysfunction.
- Interpretation and limitations
- A low C3 with relatively preserved C4 can fit alternative-pathway activation, but normal C3 does not exclude C3G and detailed assays need expert interpretation.
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Infection, autoimmune and cryoglobulin evaluation - Why
- Find a treatable generator of circulating immune complexes.
- Interpretation and limitations
- Select hepatitis testing, cultures, echocardiography, ANA-related studies and cryoglobulins from the phenotype; false-negative cryoglobulins occur if transport is mishandled.
- 05
Serum and urine monoclonal-protein assessment - Why
- Detect a small pathogenic clone that may drive MPGN or complement activation.
- Interpretation and limitations
- Combine electrophoresis or immunofixation with serum free light chains interpreted for renal function; a small clone can be significant despite absent myeloma-defining features.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Lupus nephritis
Systemic lupus features and a full-house immunofluorescence pattern favour lupus, whereas isolated C3 dominance or a specific chronic driver suggests another MPGN mechanism.
Infection-related glomerulonephritis
An acute nephritic illness around infection may resolve with complement recovery; persistent abnormalities or an MPGN biopsy pattern warrant reassessment for ongoing infection or C3 disease.
Thrombotic microangiopathy
Endothelial swelling and double contours can mimic MPGN, but platelet-rich microthrombi, haemolysis and little immune deposition support microangiopathy.
Other monoclonal deposit disease
Restricted immunoglobulin staining, organised deposits or basement-membrane deposition may indicate a distinct MGRS lesion requiring expert pathology and haematology correlation.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01ClassifyTurn a biopsy pattern into a mechanismFirst stepRenal histology is reported as membranoproliferative or mesangiocapillary.+
- 1Review immunofluorescence dominance and electron-microscopy deposit location with an experienced renal pathologist.
- 2Map immunoglobulin-associated lesions to infection, autoimmune, cryoglobulin and monoclonal-protein pathways; map C3-dominant lesions to complement assessment.
- 3Reconcile histology with serology and clinical course, seeking a second pathology opinion when classification will determine high-risk treatment.
02SearchFind the upstream driverImmune-complex MPGN or C3 glomerulopathy is suspected.+
- 1Take a detailed infection, autoimmune, haematological, family, transplant and medicine history before selecting investigations.
- 2Exclude clinically important infection and monoclonal gammopathy promptly; involve microbiology or haematology where the phenotype warrants.
- 3For C3-dominant disease, refer for specialist complement autoantibody, functional and genetic assessment rather than interpreting isolated assays locally.
03TreatMatch therapy to cause and activityThe mechanism, activity and chronicity have been reviewed by nephrology.+
- 1Provide antiproteinuric and blood-pressure care, salt advice and complication management while avoiding treatment-induced hypovolaemia.
- 2Treat an identified infection, autoimmune disease or pathogenic clone through the relevant multidisciplinary pathway before using a generic MPGN label to select therapy.
- 3Consider immunosuppression or complement-directed treatment only through current specialist guidance, NICE status, commissioning route and product safety requirements.
04PlanPrepare for recurrence and kidney failureDisease progresses despite treatment or transplantation is being considered.+
- 1Discuss kidney replacement options early enough for informed preparation rather than waiting for an emergency start.
- 2Explain that C3 glomerulopathy and some immune-complex mechanisms can recur in a graft, affecting surveillance and living-donor counselling.
- 3Link eligible patients with the UK Rare Renal Disease Registry through their nephrologist while preserving standard clinical follow-up.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
ACE inhibitor or angiotensin-receptor blocker
Begin and titrate one class according to the current CKD formulary, blood pressure, proteinuria, potassium and eGFR, with early laboratory review.Avoid dual blockade. Reassess during dehydration, sepsis, hypotension, hyperkalaemia or a large creatinine rise; pregnancy and renal-artery stenosis precautions still apply.
Disease-specific immune or complement therapy
No universal regimen is safe for an MPGN pattern. A specialist centre must select any immunosuppressive, clone-directed or complement inhibitor using the live indication, NICE decision, commissioning policy and SmPC.Exclude infection first; assess vaccination, encapsulated-organism prophylaxis where relevant, blood counts, immunoglobulins, fertility and organ-specific toxicity. Historical evidence or a trial protocol is not authority to prescribe.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Nephritic or nephrotic syndrome
Capillary inflammation causes haematuria and declining filtration, while extensive barrier injury can add heavy proteinuria, hypoalbuminaemia, oedema and thrombosis risk.
Progressive kidney failure
Persistent infection, clone activity or complement dysregulation drives irreversible glomerular and interstitial scarring with falling eGFR.
Hypertension and fluid overload
Reduced filtration and glomerular inflammation retain sodium, producing hypertension, peripheral oedema, pulmonary congestion and severe breathlessness.
Allograft recurrence
Complement-mediated and some monoclonal or immune-complex diseases may recur after transplantation, threatening graft function and influencing specialist planning.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Track creatinine, eGFR, ACR or PCR, albumin, blood pressure and urine sediment more frequently during active decline or treatment change.
- Repeat C3, C4 and validated disease biomarkers only when the specialist team has defined how results will alter management.
- Monitor the identified upstream disease, such as infection clearance, autoimmune activity or monoclonal-protein response, alongside kidney outcomes.
- Apply regimen-specific blood-count, infection, hepatic and immunisation surveillance for any immune or complement therapy.
- Reassess kidney-failure risk and replacement planning when the eGFR slope worsens, even if proteinuria transiently falls.
- After transplantation, use the transplant centre's recurrence surveillance rather than relying on serum creatinine alone.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
MPGN is architecture, not a cause
A pathology pattern is the starting point for immunofluorescence-led classification and an upstream disease search.
Dense deposit disease is a C3G subtype
The defining dense intramembranous appearance is ultrastructural and does not require the classic MPGN light-microscopy pattern.
A small clone may cause large renal harm
Monoclonal gammopathy can be kidney-significant without meeting conventional criteria for symptomatic myeloma.
Complement levels are imperfect
Concentrations reflect production and consumption and cannot replace biopsy or specialist functional assessment.
Transplant recurrence informs consent
Systemic complement dysregulation can persist after replacing the kidney, so graft risk must be discussed before transplantation.
11Common pitfallsFrequent interpretation and management errors.
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Treating the words MPGN on light microscopy as a complete diagnosis.
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Giving immunosuppression before excluding endocarditis, hepatitis or another chronic infection.
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Assuming a normal serum C3 concentration rules out C3 glomerulopathy.
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Missing MGRS because the paraprotein is small or there are no lytic lesions.
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Ordering complement genetics without expert phenotyping, consent or a plan to interpret uncertain variants.
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Presenting an emerging complement drug as routine NHS care before checking the current NICE and commissioning position.