Synopsis
Detect pauci-immune crescentic glomerulonephritis within multisystem ANCA-associated vasculitis, assess organ threat promptly, and support biopsy-led induction, prophylaxis and relapse-prevention care.
- Granulomatosis with polyangiitis and microscopic polyangiitis commonly cause necrotising pauci-immune crescentic GN; eosinophilic granulomatosis with polyangiitis affects kidneys less often but remains in the differential.
- PR3-ANCA is associated more often with GPA and relapse, while MPO-ANCA is associated more often with MPA and renal-limited disease; neither antibody defines phenotype perfectly.
- Haematuria, red-cell casts, proteinuria and a creatinine rise can be clinically silent, so urinalysis and serial renal function belong in every suspected systemic-vasculitis assessment.
- ENT inflammation, pulmonary nodules or haemorrhage, scleritis, purpura and mononeuritis multiplex are high-yield extra-renal clues, but renal-limited disease has none of them.
- ANCA may be negative in biopsy-proven pauci-immune disease and may be positive in infection, inflammatory bowel disease or drug exposure; clinical probability and biopsy matter.
- Kidney biopsy establishes the activity–chronicity balance and usually shows necrosis and crescents with little or no immune deposition on immunofluorescence.
- Active GPA or MPA requires induction immunosuppression, with rituximab or intravenous pulsed cyclophosphamide as current BSR first-line options combined with glucocorticoid or avacopan strategy.
- Reduced glucocorticoid exposure is preferred where suitable because infection and metabolic harm are major early causes of morbidity; the taper is planned from treatment day one.
- Avacopan can replace much of the glucocorticoid burden for selected active GPA or MPA under NICE and specialist criteria, but it does not replace rituximab or cyclophosphamide induction.
- Plasma exchange is not routine for every severe creatinine rise after PEXIVAS; nephrology individualises use for selected extreme renal risk, hypoxaemic alveolar haemorrhage or anti-GBM overlap.
- Rituximab is the preferred BSR maintenance option after remission, typically for 24–48 months with individual relapse and infection review; azathioprine or methotrexate may be alternatives.
- ANCA titre and B-cell count can inform context but clinical assessment, urine and kidney trajectory determine relapse; do not treat a laboratory rise in isolation.
Key red flags
Dyspnoea, hypoxia, diffuse opacities and falling haemoglobin may represent alveolar bleeding even without haemoptysis and demand critical pulmonary–renal assessment.
Painful, asymmetric, stepwise motor or sensory deficits such as foot drop indicate nerve infarction and are organ-threatening even when creatinine is normal.
Scleritis, visual change, proptosis or painful ophthalmoplegia may threaten sight and needs same-day ophthalmology and vasculitis-team review.
Investigation priorities
Identify glomerular blood, casts and protein and establish a baseline for renal response.
Management branches
AKI or falling eGFR accompanies active glomerular urine findings with or without systemic vasculitic features.
- Admit according to organ threat, assess lungs, nerves, eyes, ENT, skin and cardiovascular state, and treat hyperkalaemia, acidosis, sepsis or respiratory failure immediately.
- Send PR3, MPO, anti-GBM, complement, ANA, cultures and focused infection tests, obtain chest imaging and review medicines and cocaine exposure.
- Arrange urgent kidney biopsy when safe and hold a renal–rheumatology treatment discussion; do not let a negative ANCA delay biopsy in a convincing syndrome.
Key medicines
RituximabInduction and maintenance use a specialist intravenous protocol with premedication, screening and scheduled re-dosing.Infusion reaction, hepatitis B reactivation, hypogammaglobulinaemia, late neutropenia and serious infection require screening, immunoglobulin review and vaccine planning.
Intravenous cyclophosphamidePulse dose and interval follow the vasculitis protocol with reductions for age, eGFR, cytopenia and cumulative exposure.Myelosuppression, sepsis, infertility, teratogenicity, bladder toxicity and later malignancy require blood counts, hydration, contraception and fertility discussion.