Diagnostic Testing for Henoch-Schönlein Purpura
The diagnosis of Henoch-Schönlein purpura (HSP, now termed IgA vasculitis) is primarily clinical and does not require a single confirmatory test; however, urinalysis, blood pressure monitoring, and renal function assessment are essential at presentation and during follow-up, with skin or renal biopsy reserved for atypical presentations or significant renal involvement. 1, 2
Essential Initial Testing
Clinical Diagnosis
- HSP is identified based on palpable purpura plus at least one of the following: diffuse abdominal pain, arthritis/arthralgia, renal involvement (hematuria/proteinuria), or biopsy showing predominant IgA deposition 2
- The American College of Rheumatology criteria require any 2 or more of: age ≤20 years at onset, palpable purpura, acute abdominal pain, and biopsy showing granulocytes in small vessel walls (sensitivity 87.1%, specificity 87.7%) 3
Mandatory Laboratory Tests at Each Visit
- Urinalysis: Essential to detect hematuria and proteinuria, which indicate renal involvement 2, 4
- Blood pressure measurement: Required to identify hypertension as a marker of renal disease 4
- Estimated glomerular filtration rate (eGFR): Assess baseline and ongoing renal function 4
- Basic laboratory tests: Should be performed at each clinical visit using a structured assessment 5
Biopsy Indications
Skin Biopsy
- Consider when diagnosis is uncertain: Histopathology shows leukocytoclastic vasculitis with IgA-immune deposits in vessel walls, which increases diagnostic sensitivity and specificity 1
- Biopsy demonstrates fibrinoid necrosis with diagnostic yield over 70% when performed appropriately 5
- However, hospitals show no significant variation in skin biopsy utilization, suggesting it is not routinely performed 6
Renal Biopsy
- Indicated for patients with nephrotic/nephritic syndrome or significant persistent proteinuria: This evaluates the extent of renal inflammation 7
- International consensus guidelines now outline specific indications for renal biopsy 7
- Renal biopsy remains the gold standard for diagnosing IgA vasculitis nephritis since noninvasive confirmation is still pending 4
- Biopsy shows pauci-immune glomerulonephritis with predominant IgA deposition in glomeruli 5, 1
Additional Diagnostic Considerations
Tests with Variable Utilization
- Abdominal imaging and endoscopy: Show significant variation between hospitals (used in 36% of hospitalized cases) but are not universally required 6
- These should be reserved for patients with severe gastrointestinal symptoms or gastrointestinal bleeding 2
Tests NOT Routinely Indicated
- ANCA testing: While recommended for other forms of vasculitis 5, it is not part of the standard HSP diagnostic workup since HSP is an IgA-mediated vasculitis, not ANCA-associated
- There is no single diagnostic test to confirm HSP 8
Monitoring Protocol
Duration and Frequency
- Renal monitoring should be conducted for 6-12 months after diagnosis, even in patients without initial renal involvement 7
- Structured clinical assessment with urinalysis should occur at each clinic visit to detect new organ involvement 5
Common Pitfalls to Avoid
- Do not rely on a single test for diagnosis; HSP requires recognition of clinical manifestations 8
- Do not skip renal monitoring even if initial urinalysis is normal, as nephritis can develop later and is the most important prognostic factor determining morbidity and mortality 2
- Biopsy accessibility may limit diagnosis in some patients with atypical presentations, representing an unmet medical need 1