What laboratory and imaging investigations are indicated for a patient (child or adolescent) suspected of Henoch‑Schönlein purpura?

Investigations for Henoch-Schönlein Purpura

Primary Diagnostic Approach

The diagnosis of Henoch-Schönlein purpura (HSP, now called IgA vasculitis) is primarily clinical, requiring only targeted laboratory and imaging studies to exclude alternative diagnoses, assess renal involvement, and evaluate for complications—not to confirm the diagnosis itself. 1

Essential Initial Laboratory Tests

Screening for Renal Involvement

• Urinalysis with microscopy to detect hematuria and proteinuria, which occur in up to 50% of pediatric HSP patients and represent the most important prognostic factor 2, 1
• Serum creatinine to assess baseline kidney function, as HSP nephritis can progress to chronic renal failure in up to 20% of cases over 20 years 2
• Blood pressure measurement at every encounter, as hypertension may indicate significant renal involvement 1

Tests to Exclude Alternative Diagnoses

• Complete blood count with platelet count to confirm non-thrombocytopenic purpura and exclude thrombocytopenia, leukemia, or other hematologic causes of purpura 1, 3
• Coagulation studies (PT/PTT) if there is concern for coagulopathy or atypical bleeding patterns 1
• Basic metabolic panel to assess electrolytes and renal function 1

Skin Biopsy: When and Why

Skin biopsy with direct immunofluorescence should be performed when the clinical presentation is incomplete, atypical, or when the diagnosis is uncertain, as IgA deposits in vessel walls are the sine qua non for definitive diagnosis. 2, 4

Specific Indications for Skin Biopsy

• Purpura without other classic features (arthralgia, abdominal pain) at presentation 2
• Atypical rash distribution or morphology 4
• Need to differentiate from other forms of leukocytoclastic vasculitis 2, 4
• Delayed renal manifestations appearing years after initial symptoms 2

The biopsy should target fresh purpuric lesions (less than 24-48 hours old) and include tissue for both histology (showing leukocytoclastic vasculitis) and immunofluorescence (demonstrating IgA-dominant immune deposits in vessel walls). 2, 4

Imaging Studies

Abdominal Imaging

• Abdominal ultrasound is indicated when severe abdominal pain, gastrointestinal bleeding, or signs of intussusception are present 1, 3
• Consider CT abdomen if complications such as bowel perforation or intussusception are suspected and ultrasound is inconclusive 1

Renal Imaging

• Renal ultrasound is not routinely required unless there are abnormal urinalysis findings, elevated creatinine, or hypertension suggesting structural renal disease 1

Tests That Are NOT Routinely Indicated

• Serum IgA levels: Elevated in only 50% of cases and do not correlate with disease severity or prognosis 4
• Complement levels (C3, C4): Typically normal in HSP and more useful for excluding other vasculitides 4
• Antinuclear antibodies (ANA) or ANCA: Only if systemic lupus erythematosus or ANCA-associated vasculitis is in the differential 4
• Renal biopsy: Reserved for patients with nephrotic-range proteinuria, rapidly declining renal function, or nephritic-nephrotic syndrome, not for diagnosis of HSP itself 2, 1

Critical Pitfalls to Avoid

• Do not delay diagnosis waiting for all four classic features (purpura, arthralgia, abdominal pain, renal involvement) to appear simultaneously, as they often present sequentially over days to weeks 2, 3
• Do not assume normal initial urinalysis excludes renal involvement, as hematuria and proteinuria can develop months to years after the initial presentation 2
• Do not perform extensive endocrine or metabolic workup (aldosterone-renin ratio, catecholamines, cortisol) unless there are specific clinical features suggesting secondary hypertension beyond HSP 1
• Do not rely on clinical diagnosis alone in atypical cases, as misdiagnosis can lead to inappropriate follow-up or missed alternative serious conditions 2

Follow-Up Monitoring

• Weekly urinalysis for the first month, then monthly for 6 months, as renal involvement can appear late and disease can relapse 1
• Blood pressure monitoring at each visit during the 6-month follow-up period 1
• Repeat urinalysis and blood pressure checks at 6 and 12 months even if initial renal screening was normal, given the risk of delayed nephritis 2, 1