IgA vasculitis and post-streptococcal glomerulonephritis in

• IgA vasculitis (IgAV), formerly called Henoch-Schonlein purpura, is the commonest systemic small vessel vasculitis of childhood: a self-limited disease of the skin, gut, joints and kidneys driven by IgA-rich immune complexes.
• It usually announces itself as palpable purpura over the lower legs and buttocks in a child aged 4 to 6 years;^[1] arthralgia of the knees and ankles and colicky abdominal pain are common partners.
• The complication that matters is kidney involvement: IgA vasculitis nephritis, which behaves like IgA nephropathy on biopsy and is the reason for long-term follow-up.
• Around 20 per 100,000 children per year are affected, and only 1 to 8 per cent of children with kidney involvement progress to kidney failure, compared with 18 to 23 per cent of adults.^{[1] [3]}
• Post-streptococcal glomerulonephritis is a different, infection-triggered nephritic illness; it produces gross haematuria one to three weeks after a streptococcal sore throat, low serum C3 and subepithelial "humps" on biopsy.^[3]
• Haemolytic uraemic syndrome must be excluded whenever there is bloody diarrhoea plus anaemia and a falling platelet count: it is a thrombotic microangiopathy, not a vasculitis, and needs different treatment.^[5]

By the end of this page you should be able to:

1. Recognise the typical tetrad of IgA vasculitis and apply the EULAR/PRINTO/PReS classification criteria.
2. Distinguish IgA vasculitis nephritis from post-streptococcal glomerulonephritis and from IgA nephropathy on clinical and laboratory grounds.
3. Explain why HUS belongs in the differential of a child with purpura and renal involvement, and how it differs mechanistically and in management.
4. Plan investigations for a child with IgA vasculitis, including when to biopsy and what to monitor.
5. Outline evidence-based treatment of IgA vasculitis, its renal involvement and its relapses, and state what does not work.
6. Explain prognosis, relapse risk and required long-term follow-up to a family.

Post-infectious, usually streptococcal, glomerulonephritis is an acute immune-complex glomerulonephritis that presents with nephritic features one to three weeks after an infection, most often of the pharynx or skin.^[4]

Haemolytic uraemic syndrome is a thrombotic microangiopathy defined by the triad of microangiopathic haemolytic anaemia, thrombocytopenia and acute kidney injury. It is not a vasculitis and shares only geography with the other two conditions.

IgA vasculitis with nephritis (IgAVN) is glomerulonephritis with dominant or co-dominant IgA glomerular deposition in a patient with IgAV; on kidney biopsy it is morphologically indistinguishable from IgA nephropathy.

Nomenclature matters in practice: the older name "Henoch-Schonlein purpura" persists in records and in families, but IgAV is preferred now. The renal form is more precisely labelled IgAVN than "HSP nephritis".

The two relevant infection-related nephritides in this discussion are:

• Acute post-streptococcal glomerulonephritis (APSGN), the classic nephritic illness after group A streptococcal pharyngitis or pyoderma.
• IgA-dominant infection-related glomerulonephritis, which clinically mimics IgAN and IgAVN and must be excluded before diagnosing primary IgAN.

IgAV is the commonest systemic vasculitis of childhood. The annual incidence is estimated at 3 to 27 pediatric cases per 100,000 children,^[3] with around 20 cases per 100,000 children per year in some series.^[1] It can occur at any age, but peak presentation is between the ages of 4 and 6 years.^[1]

In adults IgAV is rare, occurring in around 2 per 100,000 adult population, with median age at diagnosis near 50 years, later onset and more kidney disease.^[1]

IgAV shows seasonal clustering in winter and spring, attributed to upper respiratory infection.^[1]

The disease is reported more often in Southeast Asian populations, matching the geography of IgA nephropathy.^[1]

Post-streptococcal glomerulonephritis and APSGN follow streptococcal disease: they are more common in school-aged children, in crowded settings and in regions where skin infection is common.

Haemolytic uraemic syndrome has a peak in children younger than 5 years. Shiga toxin-producing Escherichia coli accounts for 90 to 95 per cent of HUS cases, and the incidence of HUS among individuals infected with this organism ranges from 5 to 15 per cent.^{[5] [1]}

IgAV is thought to be a Type III hypersensitivity reaction: aberrant galactose-deficient IgA1 drives deposition of IgA-rich immune complexes in small vessel walls, activating complement and neutrophils.^[1]

Recognised triggers in children include infections, particularly of the pharynx or gut where IgA predominates: 30 to 50 per cent of pediatric cases appear to be preceded by an infection, most commonly streptococcal pharyngitis or tonsillitis.^[1] COVID-era case series suggest the trigger can be viral too.^[1]

Other proposed triggers are allergens, atopy, some medications (antibiotics, non-steroidal anti-inflammatory drugs, antihistamines), vaccinations and insect bites, but evidence is weaker.^[1]

Most cases are sporadic. A minority have a family history. There is no single modifiable risk factor to target.

The multihit hypothesis accepted for IgAV has four steps.^[1]

1. A genetically susceptible person.
2. An environmental trigger, usually an infection.
3. Production of galactose-deficient IgA1 (gd-IgA1).
4. Inflammatory endothelial injury from deposition of IgA-containing immune complexes.

The glomerular lesion is mesangial IgA deposition with more endocapillary hypercellularity and crescents than is usually seen in IgA nephropathy.^[1]

Skin, gut, joints and kidneys are preferentially affected because small vessels in those tissues receive the immune complexes. IgAVN is pathologically the renal expression of the same process, which is why it is indistinguishable from IgA nephropathy on biopsy.

• Skin: a biopsy of a fresh purpuric lesion shows leukocytoclastic vasculitis with IgA deposits in dermal vessel walls. This is most useful in atypical cases and in adults.^[1]
• Kidney: mesangial IgA with C3 deposition, with more endocapillary hypercellularity and crescents than is usually seen in IgA nephropathy. The light and immunofluorescence picture is otherwise indistinguishable from IgA nephropathy, so the diagnosis rests on the systemic features.^[3]

A child with palpable purpura over the lower legs and buttocks, who has arthralgia, colicky abdominal pain and microscopic haematuria, has IgAV until proven otherwise.

The rash is palpable purpura, usually 2 to 10 millimetres, symmetrical, and characteristically over the lower limbs and buttocks. It rarely involves the face, palms or soles. In about 5 per cent of patients the rash appears after other organ symptoms, commonly abdominal.^[1]

Polyarthralgia is common in the acute phase: symmetric pain of knees and ankles, usually colocalised with the rash. Long-term joint damage is extremely rare.^[1]

Symptoms range from fleeting colicky pain and diarrhoea to intussusception, bowel infarction and perforation. Intussusception is more common in children and rarely reported in adults.^[1]

Orchitis at presentation is linked to an extensive lower limb rash, and is much less reported in adults.^[1]

Pulmonary haemorrhage, cerebral vasculitis and neuropathies occur. Renal involvement is the complication that drives management and follow-up.

Nephritis ranges from microscopic haematuria and proteinuria to macroscopic haematuria, nephrotic-range proteinuria, hypertension and acute kidney injury. In a compiled review of 24 studies and 7,180 children with IgAV, the mean rate of nephritis was 29.9 per cent.^[1]

Currently around 1 to 8 per cent of pediatric patients and 18 to 23 per cent of adult patients progress to irreversible kidney failure despite treatment.^[1]

Peak nephritis often occurs within the first month, so monitoring must be front-loaded.

Two questions arise: what else looks like IgAV, and what else could cause a purpuric rash with renal impairment.

A teaching point: any ill, febrile child with purpura is meningococcaemia until excluded. Do not wait.

Haematology and biochemistry:

• Full blood count; platelets must be normal in IgAV, which is your first screen against ITP and TTP/HUS.
• Urea, creatinine and electrolytes; eGFR.
• Serum albumin; C3 and C4; IgA can be raised but is not diagnostic.
• Anti-streptococcal antibodies (ASOT, anti-DNase B) if post-streptococcal disease is possible.
• Urinalysis: dipstick blood and protein; first-morning urine protein:creatinine ratio; microscopy for dysmorphic red cells and casts.
• Skin biopsy of a fresh purpuric lesion can confirm leukocytoclastic vasculitis with IgA in dermal vessels in atypical cases or in adults.

Imaging is not routinely needed. Kidney ultrasound before biopsy if there is severe impairment.

The EULAR/PRINTO/PReS classification criteria for childhood IgAV (Ankara 2008) are the standard used. They require mandatory palpable purpura, predominantly on the lower limbs, with any one of:

• abdominal pain;
• acute arthritis or arthralgia;
• proteinuria or haematuria;
• histopathologic evidence of leukocytoclastic vasculitis; or
• IgA-dominant glomerulonephritis.

In the ACR review these show 100 per cent sensitivity and 87 per cent specificity against other childhood vasculitides.^[1]

Adult-onset disease has no validated criteria; application of the childhood ones has been trialled but not adopted, which is a real barrier to adult care and to trial design.^[1]

Severity in renal disease is defined by proteinuria level, eGFR and, where biopsied, the Oxford MEST-C score. The KDIGO 2025 takeaways and the IPNA 2025 recommendations discuss these. An IPNA kidney biopsy is recommended in children with IgAV and moderate proteinuria (urine protein:creatinine ratio 1 to 2 milligrams per milligram, or 100 to 200 milligrams per millimole) for 2 to 4 weeks, or mild proteinuria (0.2 to 0.5 milligrams per milligram, or 20 to 50 milligrams per millimole) for more than 4 weeks.^[3]

• Pain, arthralgia and mild abdominal pain: simple analgesia (paracetamol, ibuprofen if renal function is normal).
• Severe abdominal pain, intussusception or significant gastrointestinal bleeding: admission, analgesia, and a short course of systemic glucocorticoids is commonly used; several studies suggest a short course shortens abdominal symptoms and reduces intussusception.
• Haematuria alone needs no specific drug treatment, but does need monitoring.

• Systemic glucocorticoids should not be used to prevent nephritis in children with IgAV.^{[3] [2]}
• Heparin, dipyridamole, aspirin and montelukast should not be used to prevent nephritis.^[3]

• Monitor for the development of proteinuria for at least 12 months.^[3]
• Glucocorticoids are not recommended for IgAVN presenting as isolated microscopic or macroscopic haematuria with no proteinuria (urine protein:creatinine ratio under 0.2 milligrams per milligram, or 20 milligrams per millimole).^[3]
• Consider renin-angiotensin system blockade (ACE inhibitor or ARB) in IgAVN with proteinuria (urine protein:creatinine ratio at least 0.2 milligrams per milligram, or 20 milligrams per millimole).^[3]
• Yearly lifelong monitoring of blood pressure and urinalysis is recommended for any child with a history of IgAVN.^[3]
• At relapse of nephritis, evaluate urine sediment, protein:creatinine ratio on a first-morning urine and eGFR.^[3]
• Immunosuppressive treatment of IgAVN should run for at least 8 to 12 weeks; it can be discontinued after at least 4 weeks of remission of proteinuria (protein:creatinine ratio under 0.2 milligrams per milligram, or 20 milligrams per millimole) and absence of gross haematuria with normal eGFR (over 90 millilitres per minute per 1.73 square metres).^[3]
• Monitor children with IgAVN with urinalysis, eGFR and blood pressure for at least 5 years after the initial episode.^[3]

• Rapidly progressive IgAVN is treated in line with the KDIGO guideline for ANCA-associated vasculitis, because evidence in IgAV specifically is lacking.
• There are insufficient data on plasma exchange in IgAVN with rapidly progressive glomerulonephritis.

For adults with IgAVN the KDIGO 2025 takeaways apply alongside nephrology input. A kidney biopsy is recommended if there are signs of significant end-organ damage, proteinuria of at least 0.5 grams per day persisting for over 4 weeks, impaired kidney function, or when the diagnosis is in doubt. Proteinuria at or over 0.5 grams per day identifies an adult at increased risk of progressive loss of kidney function; management combines control of IgA immune-complex mediated injury (reduced-dose glucocorticoids with antimicrobial prophylaxis may be used after discussion) with management of nephron loss (lifestyle advice, blood pressure target 120 over 70 millimetres of mercury with RAS blockade first line, sodium restriction under 2 grams per day, SGLT2 inhibitors; renin-angiotensin and SGLT2 inhibitors singly or in combination). The International IgA Nephropathy Prediction Tools are not validated for IgAVN. Dynamic reassessment of risk is advised, and all patients should be offered clinical trial participation.^[2]

The ACR review emphasises that high-quality trial evidence in IgAVN is sparse, that steroid and immunosuppressant practice rests heavily on expert opinion, and that the IPNA 2025 recommendations and the KDIGO 2025 guideline are the current consensus frameworks. Clinicians should expect variation in practice between centres.^[1]

Acute post-streptococcal glomerulonephritis is an acute glomerulonephritis triggered by group A streptococcus, usually pharyngitis or pyoderma, presenting with the classic nephritic syndrome one to three weeks after infection. It is immune-complex mediated and self-limited in most children.^[3][4]

Gross haematuria ("cola-coloured" urine), often with oedema, hypertension, oliguria and mild renal impairment. Fever and malaise are common.

• Urinalysis: red cells, red cell casts, proteinuria, often heavy.
• Serum C3 is reduced in the acute phase and usually returns to normal over the following weeks; a persistently low C3 suggests an alternative diagnosis such as lupus nephritis or C3 glomerulopathy.^[3]
• Anti-streptococcal antibodies (ASOT and anti-DNase B, the latter preferred after skin infection) support the trigger.^[3]
• Blood urea and creatinine reflect degree of impairment.

Diffuse proliferative glomerulonephritis with subepithelial electron-dense deposits ("humps") on electron microscopy and C3 with IgG deposits on immunofluorescence.^[3] The C3-dominant or IgA-dominant immune pattern matters when distinguishing infection-related glomerulonephritis from primary IgAN and IgAVN.

• Supportive: fluid and salt restriction, diuretics for hypertension and oedema, antihypertensives as needed.
• Treat the residual infection (antibiotics if still present).
• Dialysis is rarely needed for acute kidney injury.
• Routine glucocorticoids and immunosuppressants are not used; they are reserved for atypical severe presentations and are not evidence-based.
• Most children recover fully; transient microhaematuria and proteinuria may persist for some months.
• Household contacts should have throat swabs and treatment as appropriate to limit spread.

HUS is a thrombotic microangiopathy, not a vasculitis. It appears in this topic because a child with IgAV plus bloody diarrhoea, anaemia and thrombocytopenia must be reclassified until HUS is excluded.

Key points:

• HUS is the triad of microangiopathic haemolytic anaemia, thrombocytopenia and acute kidney injury.^[5]
• Shiga toxin-producing Escherichia coli (STEC) accounts for 90 to 95 per cent of HUS, commonly after contaminated food and water; the incidence of HUS among infected individuals ranges from 5 to 15 per cent, peaking in children younger than 5 years. Bloody diarrhoea begins around day 2 to 3 after exposure, and HUS onset is 3 to 10 days after the start of diarrhoea.^[5]
• Atypical HUS (5 to 10 per cent of cases) reflects uncontrolled complement activation, genetic or acquired; it can present with bloody diarrhoea in up to 30 per cent of cases, so the presence of diarrhoea does not prove typical disease. Up to 25 per cent of HUS cases follow non-STEC infections, including Streptococcus pneumoniae.^[5]
• Neurological symptoms are common.^[5]
• TTP, HELLP syndrome and DIC are the other thrombotic microangiopathies to differentiate.^[5]
• Management differs completely from IgAV: children with STEC-HUS need supportive care and renal replacement when needed; anti-complement therapy is used in atypical HUS; platelet transfusion is avoided unless bleeding. Plasma exchange is considered in TTP, not routinely in IgAV.^[5]

This distinction protects children from receiving immunosuppression for IgAV when they actually have complement-driven microangiopathy.

Of IgAV:

• Nephritis, with progression to chronic kidney disease and rarely kidney failure.
• Severe gastrointestinal: intussusception, bowel ischaemia, perforation. Intussusception is more common in children.
• Pulmonary haemorrhage, cerebral vasculitis, seizure and neuropathy (rare).
• Orchitis.
• Chronic kidney disease in a minority, mainly adults and children with severe initial nephritis.

Of APSGN:

• Hypertensive encephalopathy, heart failure from fluid overload.
• Rapidly progressive glomerulonephritis in a minority.
• Rarely chronic kidney disease.

Of HUS:

• Neurological sequelae, chronic kidney disease.

• In children, 90 per cent have resolution of IgAV symptoms within one to two months.^[1] Kidney involvement determines long-term outlook: nephritis presents in 20 to 54 per cent of children, but only 1 to 8 per cent progress to irreversible kidney failure.^[1] Children with persistent proteinuria, impaired kidney function at presentation and hypertension fare worse.

Relapse of IgAV occurs in about 15 per cent of children and around 30 per cent of adults.^[1] Relapse does not usually imply worse long-term outcome unless renal involvement returns.

In adults, incidence is lower but outcomes are worse: more severe renal disease, more deaths with older age, severe gut or pulmonary involvement.

Post-streptococcal glomerulonephritis in children usually resolves completely, with transient urinary abnormalities for months.

HUS prognosis depends on infection type and the speed of support; atypical HUS has a risk of relapse and of chronic kidney disease requiring long-term complement blockade.

• There is no primary prevention for IgAV beyond general infection control and hygiene.
• Systemic glucocorticoids should not be used to prevent nephritis.
• Heparin, dipyridamole, aspirin and montelukast should not be used to prevent nephritis.
• Early and regular urinalysis during the first 12 months detects nephritis before it becomes severe.
• In post-streptococcal disease, treating contacts reduces further cases.
• Food hygiene, hand-washing and avoiding undercooked meat and unpasteurised products reduce STEC-HUS.

This page is written for children. Most IgAV is self-limited; the job is to detect and treat nephritis.

The same principles apply; older children can have more severe renal disease.

Adult IgAV is rare but carries a worse renal prognosis; adult pathways, adult nephrology input and biopsy thresholds apply. The KDIGO 2025 takeaways on IgAVN are largely adult-focused.

IgAV in pregnancy is uncommon. Specialist multidisciplinary care is required; data are limited and management should follow nephrology and rheumatology advice.

• Urinalysis and blood pressure measurement are the tests that matter: cheap, repeatable and predictive. They should be performed at diagnosis and at every review for at least 12 months.
• Serum C3, ASOT and biopsy are not available everywhere; in their absence, a nephritic illness 1 to 3 weeks after a sore throat with haematuria points to post-streptococcal disease, and purpura plus nephritis points to IgAV.
• RAS blockers, basic antihypertensives, diuretics and simple analgesia cover most needs; immunosuppression and renal replacement require referral.
• Consider public health measures for streptococcal skin disease where it is endemic.

• IgAV is the commonest childhood systemic vasculitis, with 3 to 27 cases per 100,000 children per year and peak age 4 to 6 years.^[1][3]
• It is a self-limited IgA immune-complex small vessel vasculitis of skin, gut, joints and kidneys.
• Diagnosis uses the EULAR/PRINTO/PReS Ankara 2008 criteria: mandatory purpura plus one of abdominal pain, arthralgia, proteinuria/haematuria, vasculitic biopsy or IgA glomerulonephritis, with 100 per cent sensitivity and 87 per cent specificity.^[1]
• Nephritis affects 20 to 54 per cent of children but only 1 to 8 per cent progress to kidney failure; monitoring proteinuria for at least 12 months is essential.^[1][3]
• Systemic steroids should not be used to prevent nephritis; heparin, dipyridamole, aspirin and montelukast do not prevent it.^[3]
• Post-streptococcal glomerulonephritis is a separate, self-limited nephritic syndrome with low C3 and subepithelial humps; management is supportive.^[3]
• HUS is a thrombotic microangiopathy with STEC in 90 to 95 per cent of cases; management is supportive and anti-complement therapy, never immunosuppression for presumed vasculitis.^[5]
• Relapse occurs in about 15 per cent of children; lifelong blood pressure and urinalysis follow-up is advised after IgAVN.^[1][3]