Urticarial Vasculitis Workup
For suspected urticarial vasculitis, obtain a lesional skin biopsy to confirm leukocytoclastic vasculitis, followed by complement levels (C3, C4), inflammatory markers (ESR, CRP), complete blood count, and antinuclear antibodies to distinguish hypocomplementemic from normocomplementemic disease and assess systemic involvement. 1, 2
Key Diagnostic Features to Identify
Clinical Red Flags
- Individual wheals lasting >24 hours is the most important clinical feature distinguishing UV from chronic spontaneous urticaria (where lesions last 2-24 hours) 1, 2, 3
- Post-inflammatory hyperpigmentation following lesion resolution 3, 4
- Painful or burning skin lesions rather than purely pruritic 4, 5
- Palpable purpura or residual bruising 6, 4
Important caveat: Up to 57% of biopsy-proven UV patients may have wheals lasting <24 hours, so do not exclude UV based on lesion duration alone 6
Associated Systemic Symptoms
- Joint/bone pain or arthralgia 1, 5
- Recurrent unexplained fever 1
- Malaise 1, 5
- These symptoms suggest potential systemic involvement requiring more aggressive workup 1, 4
Essential Diagnostic Tests
Mandatory Initial Workup
Lesional skin biopsy is essential and the gold standard for diagnosis 1, 2, 3
Complement levels (C3 and C4) to distinguish normocomplementemic from hypocomplementemic disease 1, 2
Additional Laboratory Tests
- Inflammatory markers: ESR and CRP (elevated in 76.6% of UV patients) 6, 3
- Complete blood count 3, 4
- Antinuclear antibodies (ANA) to screen for underlying autoimmune disease, particularly systemic lupus erythematosus 3, 4
- Urinalysis to detect microscopic hematuria (abnormal in 76.6% of UV patients) 6
Additional Testing for Hypocomplementemic Disease
- C1q levels and C1q autoantibodies if hypocomplementemia is present, as these may indicate more severe disease and overlap with SLE 4
- Paraproteinemia screening in adults to exclude underlying malignancy 1
Systemic Involvement Assessment
Screen for Extracutaneous Manifestations
- Extracutaneous features are present in 81% of UV patients 6
- Renal involvement: urinalysis for hematuria and proteinuria 6, 4
- Pulmonary involvement: consider chest imaging if respiratory symptoms present 4
- Gastrointestinal symptoms 4
- Ocular involvement 4
Exclude Secondary Causes
- Drug-induced UV: detailed medication history, particularly for recent drug exposures 3, 4
- Infection-associated UV: appropriate infectious workup based on clinical suspicion 3, 4
- Underlying malignancy: age-appropriate cancer screening, particularly in older patients 4
- Systemic lupus erythematosus: comprehensive autoimmune workup if ANA positive 4
Diagnostic Algorithm Summary
- Clinical suspicion based on wheals >24 hours, burning/pain, hyperpigmentation, or systemic symptoms 2, 3
- Confirm diagnosis with lesional skin biopsy showing leukocytoclastic vasculitis 1, 2
- Classify disease using complement levels (C3, C4) to distinguish normocomplementemic vs hypocomplementemic 1, 2
- Assess severity with inflammatory markers (ESR, CRP), CBC, urinalysis 6, 3
- Screen for secondary causes with ANA, medication review, age-appropriate malignancy screening 3, 4
- Evaluate systemic involvement based on complement status and clinical symptoms 4, 5
Common Pitfalls to Avoid
- Do not rely solely on clinical features: skin biopsy is essential as clinical overlap with chronic spontaneous urticaria is substantial 3, 7
- Do not delay biopsy: many physicians fail to perform skin biopsy, leading to misdiagnosis as chronic spontaneous urticaria and inadequate treatment 3
- Biopsy timing matters: obtain biopsy from lesional skin, ideally from a lesion present <24-48 hours 1
- Do not assume all UV is hypocomplementemic: only 11% have low complement levels, but this subset requires more intensive monitoring 6