IgA vasculitis

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

IgA vasculitis is an IgA-immune-complex small-vessel vasculitis affecting skin, joints, bowel and kidneys. Palpable purpura is usually symmetrical and dependent but can extend to arms and trunk. Ankle and knee arthralgia is common and non-destructive. Abdominal symptoms may precede rash, creating diagnostic uncertainty. Renal involvement ranges from microscopic haematuria to rapidly progressive crescentic glomerulonephritis.

Diagnosis is clinical in a typical presentation, supported by normal or non-causative platelets and targeted biopsy. Send cultures and treat sepsis immediately when the patient is toxic. FBC, coagulation and film identify bleeding and TMA mimics. Urine and blood pressure are mandatory even when the complaint is rash or joint pain. Serum IgA can be raised but is neither sensitive nor specific and does not replace tissue.

Biopsy strategy follows consequence. A fresh purpuric lesion sampled for routine histology and direct immunofluorescence demonstrates leukocytoclastic vasculitis with vascular IgA. Kidney biopsy is preferred when nephritis severity may justify immunosuppression because it shows mesangial IgA, crescents and chronicity. Abdominal imaging evaluates bowel complications rather than confirming immune mechanism.

Most cutaneous and joint disease resolves with supportive care. Severe abdominal symptoms can respond to glucocorticoid once intussusception, perforation and infection are excluded. Preventive steroid does not reliably stop nephritis. Renal management follows proteinuria, pressure, eGFR and pathology, with ACE inhibition or ARB and nephrology-selected immunosuppression for severe active disease. Adults need particularly careful long-term renal follow-up.

Key points

IgA vasculitis classically combines non-thrombocytopenic palpable purpura, usually on dependent legs or buttocks, with arthralgia or arthritis, abdominal pain and renal abnormality.
Check observations, full blood count and platelets, coagulation, creatinine, electrolytes, albumin, CRP, urinalysis, microscopy, ACR or PCR and blood pressure at presentation.
A normal platelet count helps distinguish vasculitic purpura from thrombocytopenic bleeding but does not exclude meningococcal sepsis or DIC early.
Skin biopsy of a fresh lesion shows leukocytoclastic vasculitis; direct immunofluorescence for IgA supports diagnosis when the phenotype is atypical.
Severe abdominal pain requires ultrasound or CT and surgical review for intussusception, ischaemia, bleeding and perforation before symptoms are attributed to uncomplicated bowel oedema.
Kidney biopsy is indicated for rapidly declining function, substantial persistent proteinuria, nephrotic or nephritic syndrome and other high-risk adult disease because histology changes treatment and prognosis.
Mild skin and joint disease is managed with hydration, activity adjustment and cautious analgesia; avoid NSAIDs when renal disease, GI bleeding or dehydration is present.
Glucocorticoid can shorten severe joint or abdominal symptoms after surgical and infectious causes are excluded but should not be given solely to prevent future nephritis.
Manage established IgA-vasculitis nephritis with pressure and proteinuria reduction, usually ACE inhibitor or ARB when appropriate, and nephrology-directed immunosuppression only for selected active severe disease.
Continue urine, protein, blood pressure and eGFR monitoring for at least six months and longer in adults or after any nephritis because renal disease can appear after the rash fades.

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

Post-infectious immune trigger

Upper-respiratory and gastrointestinal infections frequently precede disease, with mucosal IgA responses becoming dysregulated; no single organism explains all cases.

Medicine and vaccine associations

Selected medicines and immune stimuli are temporal triggers in some patients, but causality requires careful chronology and competing infection assessment.

Age and host susceptibility

IgA vasculitis is commonest in children but adults develop more severe renal disease; genetic and mucosal immune factors modify risk and recurrence.

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

1
Galactose-deficient IgA1
Abnormally glycosylated IgA1 becomes antigenic, generating circulating immune complexes that deposit in small vessels and glomerular mesangium.
2
Complement-mediated vessel injury
IgA-containing deposits activate alternative and lectin complement pathways, recruiting neutrophils and causing leukocytoclastic capillary and venular inflammation.
3
Multiorgan small-vessel leakage
Skin purpura, synovial inflammation, bowel-wall oedema and haemorrhage and glomerular blood or protein reflect the affected vascular bed.
4
Renal chronicity
Mesangial proliferation, endocapillary inflammation and crescents can progress to segmental scar and tubulointerstitial fibrosis, determining long-term kidney risk.

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

Palpable dependent purpura

Raised non-blanching lesions concentrated on legs and buttocks with normal platelets supports cutaneous small-vessel vasculitis.

Joint involvement

Transient painful swelling of ankles and knees commonly accompanies rash without erosive or permanently destructive arthritis.

Gastrointestinal vasculitisRed flag

Colicky pain, vomiting, occult or overt bleeding and bowel-wall oedema can precede purpura and may progress to intussusception.

Renal involvementRed flag

Microscopic blood, protein, hypertension, oedema or creatinine change may emerge days to weeks after other symptoms.

Red flags requiring action

Non-blanching rash with hypotension, fever, neck stiffness or rapid progression requires immediate meningococcal and sepsis treatment before vasculitis classification.
Severe colicky abdominal pain, guarding, bilious vomiting, GI bleeding or a palpable mass suggests intussusception, ischaemia or perforation.
Rising creatinine, oliguria, hypertension, nephrotic proteinuria or red-cell casts requires urgent nephrology and possible kidney biopsy.
Scrotal pain requires torsion assessment; oedema and haematuria do not make an acute scrotum automatically vasculitic.
Adult-onset disease has greater CKD risk and needs longer urine, protein, pressure and eGFR follow-up than a transient rash suggests.

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
FBC, platelets, coagulation and blood filmFirst step
Why
Distinguish non-thrombocytopenic vasculitis from platelet, DIC and microangiopathic bleeding disorders.
Interpretation and limitations
Normal platelets support IgA vasculitis but do not exclude early sepsis; schistocytes or coagulopathy redirects emergency care.
02
Urinalysis, microscopy, ACR or PCR and serial eGFR
Why
Detect nephritis, quantify protein and establish renal trajectory.
Interpretation and limitations
Glomerular blood, casts and protein indicate renal involvement; repeat after rash resolution because nephritis may appear later.
03
Skin biopsy with direct immunofluorescence
Why
Confirm leukocytoclastic vasculitis and vascular IgA in atypical or adult disease.
Interpretation and limitations
Sample a fresh lesion, with separate handling for immunofluorescence; older lesions lose diagnostic deposits and IgA is supportive, not entirely specific.
04
Kidney biopsy
Why
Grade active crescents and chronic scar when renal severity may warrant immunosuppression.
Interpretation and limitations
Biopsy is the reference renal assessment for rapidly progressive, nephrotic or persistently proteinuric disease and separates other glomerulonephritis.
05
Abdominal ultrasound or CT
Why
Identify intussusception, bowel-wall oedema, ischaemia, perforation and alternative surgical disease.
Interpretation and limitations
Ultrasound is useful for intussusception, while CT better defines adult bowel and vascular complications; imaging does not replace surgical assessment.
06
Complement, ANA, ANCA, infection and cryoglobulin tests
Why
Investigate atypical systemic disease, low complement, adult onset or an alternative small-vessel mechanism.
Interpretation and limitations
Choose tests from phenotype; a broad negative panel does not prove IgA vasculitis and infection-associated IgA deposits occur.

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

Sepsis and meningococcal disease

A toxic patient with rapidly evolving non-blanching rash is treated immediately for sepsis; distribution and IgA tests must not delay antibiotics.

Other small-vessel vasculitis

ANCA disease, cryoglobulinaemia, lupus and hypersensitivity vasculitis cause purpura and renal or systemic injury with different serology and biopsy deposits.

Thrombocytopenia and coagulopathy

ITP, TTP, DIC, anticoagulation and haematological disease produce non-blanching lesions through bleeding rather than vessel-wall IgA inflammation.

IgA nephropathy

IgA nephropathy shares renal biology but lacks the defining systemic purpura, abdominal and joint vasculitic syndrome at presentation.

Additional chapter-specific clues

Septic purpura mimicRed flag

Toxic physiology, fever and rapidly spreading petechiae or ecchymoses require immediate sepsis treatment regardless of a possible vasculitis history.

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

01First-line assessmentConfirm purpura and screen every organFirst stepFirst linePalpable non-blanching rash occurs with joint, abdominal or urinary symptoms.

1Assess sepsis physiology first, then map rash, joints, abdomen, oedema, scrotum, pressure and urine and review infection and medicines.
2Obtain blood count, platelets, coagulation, renal, albumin, inflammatory markers, microscopy and quantitative protein.
3Use fresh skin biopsy when atypical and establish a written renal-monitoring schedule even if initial urine is normal.

02Bowel emergencyImage before assuming benign oedemaAbdominal pain is severe, focal, colicky, bleeding or accompanied by vomiting or peritonism.

1Resuscitate, provide analgesia, obtain blood count, lactate and crossmatch and involve paediatric or adult surgery according to age.
2Use urgent ultrasound for suspected intussusception and CT for adult ischaemic, bleeding or perforation questions.
3After surgical and infectious emergencies are addressed, use specialist glucocorticoid for severe vasculitic bowel symptoms and monitor recurrence.

03Renal escalationQuantify, protect and biopsy high-risk nephritisEscalationProteinuria, hypertension, eGFR decline, nephritic or nephrotic syndrome develops.

1Repeat clean urine microscopy, ACR or PCR, creatinine, albumin, pressure and oedema and exclude infection and another glomerular disease.
2Start ACE inhibitor or ARB for persistent proteinuria and pressure when renal, potassium and pregnancy status allow, with early nephrology referral.
3Biopsy rapidly progressive, nephrotic or substantial persistent proteinuric disease and use pathology-directed immunosuppression rather than steroid solely for the rash.

04Long-term follow-upContinue after the rash fadesInitial systemic symptoms resolve or renal abnormality has occurred.

1Check pressure and urinalysis weekly or fortnightly early, then monthly through at least six months according to the local age-specific pathway.
2Continue eGFR and quantitative protein monitoring longer in adults and anyone with previous nephritis, hypertension or persistent urine abnormality.
3Refer recurrent purpura, rising protein, pressure or renal decline promptly and maintain CKD cardiovascular and pregnancy counselling.

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

First analgesic for joint and abdominal discomfort when serious bowel pathology has been excluded.

Paracetamol

Use 500 mg–1 g orally up to four times daily when required, at least four hours apart, maximum 4 g in 24 hours, reducing the maximum for low body weight, liver risk or frailty.

Count all combination products and avoid overdose; review liver disease, alcohol, malnutrition and body weight. Analgesia must not delay assessment of peritonism or renal deterioration.

Shortens severe inflammatory abdominal or joint symptoms but is not prescribed simply to prevent future nephritis.

Prednisolone for severe abdominal or joint disease

After surgical and infectious emergencies are excluded, specialists may use 1 mg/kg orally once daily, commonly up to 60 mg/day, for one to two weeks followed by a taper based on response.

Monitor infection, GI bleeding, glucose, pressure, mood and bone and reassess pain that fails to improve. Do not allow symptom suppression to obscure intussusception or perforation.

Reduces intraglomerular pressure and protein loss and supports long-term renal protection in IgA-vasculitis nephritis; use below the product's macroproteinuria threshold follows nephrology guidance and may be off-label.

Ramipril for persistent renal proteinuria

For adult non-diabetic proteinuric kidney disease, start 1.25 mg orally once daily, increase to 2.5 mg after two weeks and then 5 mg after a further two weeks if tolerated; reduce the ceiling in renal or hepatic impairment.

Check creatinine and potassium before and one to two weeks after start or titration; review volume depletion, hyperkalaemia, bilateral renal-artery stenosis and angioedema. Stop before conception and immediately if pregnancy occurs.

Emergency anti-inflammatory component for selected rapidly progressive IgA-vasculitis nephritis, not routine cutaneous disease.

Intravenous methylprednisolone for rapidly progressive nephritis

For biopsy-supported severe crescentic disease, nephrology may give 500 mg–1 g intravenously once daily for three days before an oral and steroid-sparing regimen.

Obtain cultures and biopsy where safe, monitor rhythm, pressure, glucose, psychiatric, infection and GI effects and combine only with a defined nephrology treatment and taper plan.

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

Chronic kidney disease

Persistent proteinuria, hypertension, reduced eGFR and crescentic nephritis can lead to CKD and kidney failure, particularly after adult disease.

Intussusception and bowel injury

Bowel-wall oedema creates a lead point for intussusception, while vasculitis can cause haemorrhage, ischaemia, perforation and pancreatitis.

Scrotal and rare organ disease

Scrotal oedema, orchitis, CNS disease, pulmonary haemorrhage and cardiac involvement are uncommon but require urgent alternative exclusion and organ care.

Relapse and treatment harm

Purpura, joints and abdominal symptoms can recur, while unnecessary glucocorticoid exposes infection and metabolic toxicity without preventing later nephritis.

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

Check urine and pressure repeatedly for at least six months after onset even when the initial renal screen and rash outcome are reassuring.
In adults and established nephritis follow eGFR, ACR or PCR, albumin, pressure and cardiovascular risk beyond six months according to renal trajectory.
Record rash recurrence, joint function, abdominal pain, bleeding, weight and scrotal or neurological symptoms at clinical reviews.
After ACE inhibitor start or titration repeat creatinine and potassium within one to two weeks and provide pregnancy and dehydrating-illness advice.
Follow biopsy-directed immunosuppression with FBC, renal, liver, infection, vaccination, bone and reproductive safety.
Give urgent return instructions for septic physiology, severe abdominal pain, bleeding, reduced urine, oedema, headache or hypertension.

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

The rash can come second

Abdominal pain or arthritis may precede purpura, so repeat skin and urine examination when the early diagnosis remains uncertain.

Platelets should not explain the purpura

IgA vasculitis classically has a normal platelet count; thrombocytopenia demands a bleeding, sepsis or microangiopathy pathway.

Steroid does not vaccinate kidneys

Treating rash or abdominal symptoms has not reliably prevented later nephritis, making scheduled urine and pressure checks essential.

Adults carry greater renal risk

Adult disease is less common but more likely to leave proteinuria, hypertension, CKD and kidney failure than typical childhood disease.

Skin and kidney biopsies answer different questions

Skin supports the systemic IgA mechanism; kidney tissue grades active crescents and chronic scar to guide renal treatment.

11Common pitfallsFrequent interpretation and management errors.

01
Reassuring a toxic patient with purpura before treating possible meningococcal sepsis.
02
Omitting urine and pressure because the presentation is limited to rash and ankles.
03
Using a normal initial urinalysis to cancel follow-up.
04
Giving glucocorticoid solely to prevent nephritis.
05
Attributing severe colicky abdominal pain to vasculitis without imaging for intussusception or ischaemia.
06
Using NSAIDs in a dehydrated patient with GI bleeding or renal involvement.