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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Membranoproliferative and C3 glomerulopathy

Renal · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

An MPGN-pattern illness with pulmonary oedema, severe hypertension, oliguria, rapidly rising creatinine, hyperkalaemia or suspected sepsis needs same-day hospital assessment. Stabilise the complication and involve nephrology; complement investigations and genetic work-up must not delay treatment of kidney failure or infection.

Overview

Interpret an MPGN biopsy pattern mechanistically, identify immune-complex and complement drivers, and route rare C3 disease to specialist care.

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

Aetiology

01

Chronic infection

Persistent microbial antigen from deep infection, endocarditis or chronic viral disease can drive circulating immune complexes and an MPGN pattern.

02

Autoimmune and cryoglobulin disease

Systemic autoimmunity and cryoglobulinaemia generate immunoglobulin-containing complexes that deposit in glomerular capillaries and activate complement pathways.

03

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.

04

Alternative-complement dysregulation

Acquired complement autoantibodies or genetic pathway defects can sustain C3 activation, producing C3 glomerulonephritis or dense deposit disease.

Pathophysiology

  1. 1
    Immune or complement deposition

    Immunoglobulin-containing complexes or predominantly C3 fragments accumulate in mesangial and capillary-wall compartments throughout affected glomeruli during active disease.

  2. 2
    Mesangial and endothelial injury

    Complement activation and inflammatory recruitment cause mesangial proliferation, endocapillary narrowing and leakage of blood and protein.

  3. 3
    Capillary-wall remodelling

    Mesangial cells and matrix extend around deposits, creating duplication or double-contour appearances that define the membranoproliferative light-microscopy pattern.

  4. 4
    Progressive glomerular scarring

    Uncontrolled driver activity produces sclerosis, tubular atrophy and interstitial fibrosis, converting active nephritic or nephrotic disease into chronic kidney impairment.

Clinical features and red flags

Mixed nephritic–nephrotic picture

Haematuria, proteinuria, hypertension, oedema and reduced kidney function often coexist rather than forming a purely nephritic presentation.

Rapid functional lossRed flag

Oliguria, accelerating creatinine, severe hypertension or fluid overload may reflect active proliferative injury and requires urgent nephrology assessment.

Chronic infection signalRed flag

Fever, cardiac murmur, injected-drug exposure, indwelling infection or hepatitis risk should redirect evaluation before immunosuppression is contemplated.

Cryoglobulinaemic phenotype

Purpura, neuropathy, arthralgia, low complement and systemic symptoms suggest cryoglobulin-associated immune-complex disease requiring careful sample handling.

Complement-associated features

Partial lipodystrophy, retinal drusen, family clustering or recurrence after transplant supports specialist assessment for alternative-pathway dysregulation.

Investigations

  1. 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.
  2. 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.
  3. 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.
  4. 04
    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.

Differential diagnosis

01

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.

02

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.

03

Thrombotic microangiopathy

Endothelial swelling and double contours can mimic MPGN, but platelet-rich microthrombi, haemolysis and little immune deposition support microangiopathy.

04

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.

Management

01ClassifyTurn a biopsy pattern into a mechanismFirst stepRenal histology is reported as membranoproliferative or mesangiocapillary.+
  1. 1Review immunofluorescence dominance and electron-microscopy deposit location with an experienced renal pathologist.
  2. 2Map immunoglobulin-associated lesions to infection, autoimmune, cryoglobulin and monoclonal-protein pathways; map C3-dominant lesions to complement assessment.
  3. 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.+
  1. 1Take a detailed infection, autoimmune, haematological, family, transplant and medicine history before selecting investigations.
  2. 2Exclude clinically important infection and monoclonal gammopathy promptly; involve microbiology or haematology where the phenotype warrants.

Complications

01

Nephritic or nephrotic syndrome

Capillary inflammation causes haematuria and declining filtration, while extensive barrier injury can add heavy proteinuria, hypoalbuminaemia, oedema and thrombosis risk.

02

Progressive kidney failure

Persistent infection, clone activity or complement dysregulation drives irreversible glomerular and interstitial scarring with falling eGFR.

03

Hypertension and fluid overload

Reduced filtration and glomerular inflammation retain sodium, producing hypertension, peripheral oedema, pulmonary congestion and severe breathlessness.

04

Allograft recurrence

Complement-mediated and some monoclonal or immune-complex diseases may recur after transplantation, threatening graft function and influencing specialist planning.

Monitoring and follow-up

  • 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.

Special situations

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.

Common pitfalls

  1. 01

    Treating the words MPGN on light microscopy as a complete diagnosis.

  2. 02

    Giving immunosuppression before excluding endocarditis, hepatitis or another chronic infection.

  3. 03

    Assuming a normal serum C3 concentration rules out C3 glomerulopathy.

  4. 04

    Missing MGRS because the paraprotein is small or there are no lytic lesions.

  5. 05

    Ordering complement genetics without expert phenotyping, consent or a plan to interpret uncertain variants.

  6. 06

    Presenting an emerging complement drug as routine NHS care before checking the current NICE and commissioning position.

Practice

Two practice questions

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Question 1 of 2
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RenalOriginal SBA

Interpreting the biopsy label

A biopsy shows an MPGN pattern with immunoglobulin and complement deposition. What is the most appropriate next diagnostic principle?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • UKKA MPGN, DDD and C3 glomerulopathy clinician informationUK classification, causes, complement investigation and recurrence overview.
  • UKKA eCKD GuideProteinuria, progression and supportive CKD management framework.
  • NICE CKD assessment and managementReferral, monitoring, cardiovascular and renin–angiotensin recommendations.
  • NHS England renal servicesCurrent specialised commissioning route, including recurrent C3G after transplant.

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

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
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.
  • 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.
  • 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.+
    1. 1Provide antiproteinuric and blood-pressure care, salt advice and complication management while avoiding treatment-induced hypovolaemia.
    2. 2Treat an identified infection, autoimmune disease or pathogenic clone through the relevant multidisciplinary pathway before using a generic MPGN label to select therapy.
    3. 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.+
    1. 1Discuss kidney replacement options early enough for informed preparation rather than waiting for an emergency start.
    2. 2Explain that C3 glomerulopathy and some immune-complex mechanisms can recur in a graft, affecting surveillance and living-donor counselling.
    3. 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+
    Reduces glomerular pressure and proteinuria as supportive treatment across several MPGN mechanisms.

    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.

    Targets the upstream immune-complex, clonal or complement mechanism when evidence and individual activity justify treatment.

    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.