Nephritic syndrome and rapidly progressive glomerulonephritis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Glomerular capillary inflammation allows red cells and protein into urine and reduces filtration. Salt retention produces oedema and hypertension, while severe capillary-wall injury generates cellular crescents as proliferating cells compress the glomerular tuft. The faster the creatinine rises, the smaller the window to prevent fibrous, irreversible scarring.

Syndrome recognition precedes disease naming. A patient with cola urine, rising creatinine and red-cell casts has a nephritic process even before ANCA or complement returns. Conversely, a positive ANCA in a patient with bland urine is not proof of renal vasculitis. Serology, clinical organs and biopsy must tell one coherent story.

Pulmonary-renal presentation narrows the urgent differential to ANCA vasculitis, anti-GBM disease, lupus and selected infection or drug causes. Stabilise oxygenation, anaemia, potassium and fluid while sending both anti-GBM and ANCA because double-positive disease occurs. Early nephrology, respiratory, rheumatology and plasma-exchange access can determine survival and kidney recovery.

Key points

Nephritic syndrome combines glomerular haematuria, variable proteinuria, reduced GFR, sodium retention, oedema and hypertension; not every component is present.
Dysmorphic red cells and red-cell casts strongly support glomerular bleeding, while dipstick blood without red cells suggests haemoglobin or myoglobin instead.
Rapidly progressive glomerulonephritis is a clinical trajectory of kidney function loss over days to weeks, usually with crescentic injury on biopsy.
The three immune patterns are anti-GBM linear antibody disease, pauci-immune ANCA-associated disease and immune-complex disease such as lupus, IgA or infection-related GN.
Normal complement supports but does not prove ANCA or anti-GBM disease; low C3 and/or C4 directs attention toward immune-complex and complement-mediated causes.
Pulmonary haemorrhage can present with breathlessness, falling haemoglobin and diffuse opacities without visible haemoptysis, especially after alveolar blood is swallowed.
Send ANCA with PR3 and MPO, anti-GBM, ANA, dsDNA, complement, immunoglobulins and infection studies urgently while arranging renal biopsy.
Blood cultures and echocardiographic assessment matter when endocarditis is possible because infection-related GN can be worsened catastrophically by blind immunosuppression.
Biopsy determines crescents, necrosis, immune deposition and chronic scarring, which changes whether intensive immunosuppression can still recover function.
Supportive treatment of hyperkalaemia, pulmonary oedema and severe pressure runs alongside cause-specific therapy; dialysis does not replace immune treatment when recovery is plausible.
Cyclophosphamide, rituximab, plasma exchange and high-dose glucocorticoid are specialist treatments with major infection, fertility and cytopenia safeguards, not empirical ward prescriptions.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Anti-GBM antibody disease

Autoantibodies against glomerular basement membrane produce linear immune staining, rapidly progressive crescentic nephritis and sometimes simultaneous alveolar haemorrhage.

Pauci-immune vasculitis

PR3- or MPO-associated small-vessel inflammation causes necrotising crescents with little immune deposition and may involve lungs, ENT tract, skin, eyes or nerves.

Immune-complex glomerulonephritis

Lupus, IgA disease, infection-related nephritis and complement disorders deposit immunoglobulin or complement, producing varied serology and biopsy patterns.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Glomerular capillary inflammation
Antibody, immune-complex or neutrophil-mediated injury disrupts capillary walls, allowing dysmorphic erythrocytes and protein to enter filtrate.
2
Filtration loss and salt retention
Glomerular inflammation and necrosis reduce filtration, while retained sodium causes hypertension, oedema and sometimes pulmonary congestion.
3
Crescent formation
Severe capillary-wall injury generates cellular crescents; proliferating cells then compress the glomerular tuft and accelerate filtration loss.
4
Irreversible scarring
Uncontrolled active crescents become fibrous, while glomerulosclerosis and interstitial fibrosis progressively limit the kidney's capacity to recover.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Glomerular urine sediment

Visible or microscopic haematuria with dysmorphic erythrocytes, acanthocytes and red-cell casts points to glomerular capillary injury, especially when protein and creatinine rise together.

Rapid kidney trajectoryRed flag

Creatinine rising across days or weeks, oliguria, new acidosis or potassium elevation indicates RPGN and warrants same-day nephrology even if the absolute creatinine remains modest.

Pulmonary haemorrhageRed flag

New hypoxia, diffuse bilateral opacities and falling haemoglobin with active urine sediment may be alveolar bleeding; haemoptysis can be absent and anticoagulation can amplify danger.

Systemic small-vessel vasculitis

Purpura, mononeuritis multiplex, sinus disease, otitis, pulmonary nodules, scleritis, constitutional symptoms or mesenteric ischaemia supports ANCA-associated systemic inflammation.

Immune-complex phenotype

Low complement, photosensitive rash, arthritis, infection, cryoglobulinaemic features, chronic viral risk or a recent streptococcal syndrome points toward immune-complex rather than pauci-immune GN.

Hypertensive fluid emergencyRed flag

Headache, visual disturbance, encephalopathy, pulmonary oedema or severe pressure with AKI requires controlled emergency blood-pressure and volume treatment while the renal cause is investigated.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

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
Urinalysis, microscopy and ACR or PCRFirst step
Why
Confirm active glomerular sediment and quantify protein loss.
Interpretation and limitations
Dysmorphic red cells and casts support glomerulonephritis; protein may be sub-nephrotic or nephrotic, and a negative nitrite does not exclude infection-related disease.
02
Serial creatinine, urea and electrolytes
Why
Measure progression and identify urgent metabolic complications.
Interpretation and limitations
Rate of change matters; potassium, bicarbonate and fluid status determine immediate dialysis or critical-care needs while immune testing proceeds.
03
ANCA with PR3 and MPO specificity
Why
Support diagnosis and phenotype of pauci-immune small-vessel vasculitis.
Interpretation and limitations
PR3 or MPO positivity increases probability in the right syndrome, but infection, drugs and other inflammation can produce ANCA; biopsy remains important and ANCA-negative disease exists.
04
Anti-GBM antibody
Why
Identify a time-critical antibody-mediated pulmonary-renal disease.
Interpretation and limitations
A positive result with compatible renal or lung disease can justify immediate plasma-exchange pathway; send ANCA simultaneously because double positivity changes relapse follow-up.
05
ANA, anti-dsDNA, C3 and C4
Why
Assess lupus and immune-complex activity.
Interpretation and limitations
High dsDNA and falling complement support lupus nephritis but do not assign biopsy class; isolated positive ANA is common and cannot explain RPGN alone.
06
Blood cultures, viral serology and infection evaluation
Why
Find endocarditis, hepatitis, HIV or another infection causing immune-complex GN.
Interpretation and limitations
Culture before antibiotics when safe, obtain echocardiography for credible endocarditis and avoid premature immunosuppression until life-threatening infection is actively addressed.
07
Chest imaging, blood gas and haemoglobin trend
Why
Detect pulmonary haemorrhage, oedema or infection in a pulmonary-renal syndrome.
Interpretation and limitations
Diffuse opacities plus haemoglobin fall and hypoxaemia support alveolar bleeding but overlap with oedema and pneumonia; respiratory and critical-care assessment is urgent.
08
Urgent native kidney biopsy
Why
Define immune pattern, crescent burden, necrosis and reversible versus chronic damage.
Interpretation and limitations
Linear IgG suggests anti-GBM, pauci-immune necrosis supports ANCA disease and granular deposits indicate immune-complex GN; chronic sclerosis limits likely recovery.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Acute tubular injury

Shock, sepsis or toxin exposure with coarse granular casts favours tubular damage; red-cell casts, albuminuria and systemic immune features favour glomerular inflammation.

Thrombotic microangiopathy

Thrombocytopenia, schistocytes and biochemical haemolysis suggest small-vessel thrombosis, though malignant hypertension can create both endothelial and glomerular injury.

Acute interstitial nephritis

A medicine timeline, sterile pyuria and possible hypersensitivity features support interstitial inflammation; substantial glomerular haematuria or red-cell casts point away from isolated AIN.

Pigment nephropathy

Dipstick blood with few urinary erythrocytes and a muscle-injury or haemolysis context indicates myoglobin or haemoglobin rather than glomerular bleeding.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01First hoursStabilise and phenotype RPGNFirst stepActive urine sediment accompanies a rapid creatinine rise.

1Call nephrology, perform ABCDE and assess urine output, potassium, acidosis, severe pressure, pulmonary oedema, anaemia, rash, neurological and respiratory involvement.
2Send urgent urine microscopy, protein quantification, ANCA-PR3/MPO, anti-GBM, ANA-dsDNA, complement, immunoglobulins, cultures and infection serology before immune treatment when feasible.
3Arrange ultrasound to exclude obstruction and urgent biopsy, while treating hyperkalaemia, fluid overload, sepsis and dialysis indications without waiting for a final immune label.

02Pulmonary-renalTreat threatened lung and kidneyHypoxia or pulmonary opacities accompany haemoglobin fall and glomerulonephritis.

1Involve critical care, respiratory and nephrology, support oxygenation, reverse unsafe anticoagulation where indicated and distinguish haemorrhage from oedema or infection rapidly.
2Send both anti-GBM and ANCA immediately and arrange access to biopsy and plasma exchange, taking treatment samples before therapy only when no dangerous delay results.
3Begin specialist-directed glucocorticoid and cause-specific induction when clinical probability is high, adding plasma exchange for anti-GBM and selected current-guideline indications.

03Immune patternMatch induction to mechanismSerology and biopsy identify anti-GBM, pauci-immune or immune-complex disease.

1Use plasma exchange plus glucocorticoid and cyclophosphamide for treatable anti-GBM disease under the renal protocol, accounting for chronicity and pulmonary haemorrhage.
2Use current BSR and renal guidance for ANCA induction with rituximab or cyclophosphamide plus reduced glucocorticoid strategies and prophylaxis.
3Treat lupus, infection-related, IgA or complement-mediated GN according to biopsy class and cause; immunosuppression is not interchangeable across these diagnoses.

04SupportPrevent secondary kidney and lung injuryOedema, hypertension, electrolyte disturbance or uraemia complicates nephritic disease.

1Restrict sodium, use loop diuretic carefully for congestion and control blood pressure without causing renal hypoperfusion; avoid NSAIDs, contrast and other nephrotoxins.
2Treat infection, anaemia and thrombosis or bleeding risk individually, and provide gastric, bone, vaccination and Pneumocystis prophylaxis with intensive immunosuppression.
3Start dialysis for refractory potassium, acidosis, overload or uraemic complications, while continuing disease-specific therapy when renal recovery remains plausible.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Rapidly suppresses destructive glomerular and pulmonary capillary inflammation while definitive induction takes effect.

Intravenous methylprednisolone and oral glucocorticoid induction

Use the biopsy- and diagnosis-specific renal or rheumatology protocol, often beginning with one to three supervised intravenous pulses followed by a reduced-exposure oral taper rather than an unreviewed fixed course.

Exclude and treat infection, monitor glucose, mental state, blood pressure, fluid, GI and bone risk, and provide prophylaxis. Steroid alone is inadequate for anti-GBM or organ-threatening ANCA disease.

Controls antibody-producing and autoreactive lymphocyte pathways in selected crescentic anti-GBM, ANCA or immune-complex disease.

Cyclophosphamide or rituximab induction

Use only the current specialist weight-, age- and kidney-adjusted intravenous or oral cyclophosphamide schedule, or the licensed vasculitis rituximab infusion regimen, with pharmacy verification and cumulative-dose tracking.

Assess infection, hepatitis, immunoglobulins, cytopenia, bladder toxicity, malignancy, fertility and pregnancy. Provide Pneumocystis prophylaxis and vaccination planning; rituximab infusion reactions and late hypogammaglobulinaemia need monitoring.

Relieves sodium-driven oedema and pulmonary congestion while immune disease is treated.

Loop diuretic for pulmonary or peripheral congestion

Give an oral or intravenous furosemide dose matched to prior exposure, GFR and severity, reassessing urine response within hours and escalating through the local AKI or diuretic-resistance pathway.

Diuresis cannot correct inflammatory filtration loss and may worsen hypovolaemia. Monitor pressure, weight, urine, sodium, potassium and hearing at high intravenous exposure; start dialysis when refractory overload threatens.

Reduces Pneumocystis pneumonia risk during intensive remission-induction immunosuppression.

Co-trimoxazole Pneumocystis prophylaxis

Use the renal-unit prophylactic strength and schedule during cyclophosphamide, rituximab and substantial glucocorticoid exposure, adjusting for kidney function, cytopenia, allergy and local policy.

Can cause hyperkalaemia, creatinine change, rash and marrow suppression and interacts dangerously with methotrexate. Select an alternative with microbiology or pharmacy when contraindicated.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Rapid irreversible kidney failure

Extensive active crescents can replace viable glomeruli over days to weeks, leaving dialysis dependence if treatment follows established fibrous scarring.

Hyperkalaemia, acidosis and uraemia

Abrupt filtration loss retains potassium, acid and uraemic solutes, creating cardiac, neurological and pericardial emergencies independent of the immune diagnosis.

Hypertensive pulmonary oedema

Sodium retention and severe hypertension raise pulmonary capillary pressure, causing breathlessness and hypoxaemia that can accompany relatively modest peripheral oedema.

Pulmonary haemorrhage

Anti-GBM and ANCA disease may injure alveolar capillaries, producing falling haemoglobin, diffuse opacities and respiratory failure even without haemoptysis.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Trend creatinine, urine output, potassium, bicarbonate, weight and respiratory status at a frequency matched to the rapidity of change, often several times daily initially.
Repeat urinalysis and protein quantification to follow glomerular activity, recognising that microscopic haematuria can persist after systemic inflammation improves.
Monitor haemoglobin, chest imaging and oxygen requirement in pulmonary haemorrhage; visible haemoptysis is an unreliable measure of ongoing alveolar blood loss.
During induction, follow full blood count, liver tests, immunoglobulins, infection, glucose and cumulative cyclophosphamide exposure through the disease protocol.
Track disease-specific serology such as anti-GBM titre, ANCA context, dsDNA and complement as adjuncts, never as sole permission to treat or withhold therapy.
Review fertility preservation, contraception, vaccination, bone, gastric and Pneumocystis prevention before or immediately after emergency induction begins.
After remission, establish relapse symptoms, maintenance therapy, CKD cardiovascular care and a named monitoring interval across nephrology and rheumatology.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Trajectory beats threshold

A creatinine rising from 70 to 150 in days can represent more urgent glomerular loss than a stable value of 250 from longstanding CKD.

Haemoptysis can be absent

Alveolar blood may remain distal or be swallowed; falling haemoglobin, hypoxaemia and new diffuse opacities can reveal pulmonary haemorrhage first.

ANCA is not a biopsy

Infection and drugs can cause ANCA, while some pauci-immune vasculitis is antibody-negative; urine, organs and histology establish renal disease.

Complement is a routing test

Low C3 or C4 redirects the differential toward immune-complex and complement disease but does not by itself distinguish lupus, infection and C3 glomerulopathy.

Dialysis does not end reversibility

Severe crescentic disease may need temporary dialysis and still recover with timely immune treatment, depending on biopsy chronicity and clinical mechanism.

11Common pitfallsFrequent interpretation and management errors.

01
Waiting for every antibody result before calling nephrology in a rapid decline.
02
Using dipstick blood alone without urine microscopy or myoglobin context.
03
Assuming no haemoptysis means no pulmonary haemorrhage.
04
Giving blind immunosuppression without cultures when endocarditis is credible.
05
Calling a positive ANCA renal vasculitis despite bland urine and another diagnosis.
06
Interpreting normal complement as proof of pauci-immune disease.
07
Delaying dialysis because disease-specific therapy has just started.
08
Starting cyclophosphamide without fertility, infection, blood-count and prophylaxis planning.