From the Guidelines
Laboratory tests for hives (urticaria) and angioedema should be tailored to the clinical presentation, with a focused approach rather than extensive testing, as recommended by the most recent guidelines 1. Initial evaluation should include a complete blood count with differential, erythrocyte sedimentation rate or C-reactive protein, and comprehensive metabolic panel.
- For chronic cases (lasting over 6 weeks), additional testing may include:
- Thyroid function tests (TSH, free T4) to rule out thyroid disease
- Complement C4 level to screen for hereditary angioedema
- In cases of suspected allergic triggers, specific IgE testing or skin prick tests may be appropriate, as supported by studies on allergic rhinitis 1 and urticaria 1.
- For patients with angioedema without urticaria, especially with a family history, C1 inhibitor level and function tests are essential, as emphasized in guidelines for hereditary angioedema 1.
- Tryptase levels can be useful during acute episodes to evaluate for mast cell disorders or anaphylaxis, but must be drawn within 4 hours of symptom onset. These tests help distinguish between different causes of urticaria and angioedema, including allergic reactions, autoimmune conditions, hereditary disorders, and idiopathic forms, allowing for appropriate treatment strategies, as outlined in recent clinical practice guidelines 1. Most cases of acute urticaria are self-limited and don't require extensive laboratory evaluation.
From the Research
Laboratory Tests for Hives and Angioedema
- Laboratory tests are commonly ordered to identify or rule out a cause in patients with chronic urticaria/angioedema (CUA) 2
- The results of these tests are usually within normal limits or unremarkable, with abnormalities commonly seen in complete blood counts (34%) and in complete metabolic panels (9.4%) 2
- Among the tests ordered, results of 17% were abnormal, but only 1.60% of tests led to further testing and a change in management 2
Allergy Testing for Hives and Angioedema
- Allergy testing can be used to evaluate type I or type IV hypersensitivity reactions, which can cause hives and angioedema 3
- The skin prick test (in vivo) or serum IgE (in vitro) test methods can be used to evaluate type I reactions, while the skin patch test method can be used to evaluate type IV reactions 3
- Allergy testing can help identify the allergens responsible for a specific reaction, which can inform avoidance measures and treatment 3
Diagnosis and Work-up of Urticaria
- Urticaria is a common clinical condition presenting with wheals (hives), angioedema, or both, and has a complex pathogenesis 4
- The diagnosis and work-up of urticaria involve a comprehensive approach, taking into account the patient's medical history, physical examination, and laboratory tests 4
- The prognosis and outcome of urticaria is generally very favorable for most patients, but some patients may require referral to a specialist for further evaluation and treatment 5
Treatment of Urticaria and Angioedema
- Chronic urticaria and angioedema are often managed using a stepwise approach, with dose escalation of second-generation antihistamines, followed by use of omalizumab and finally cyclosporine in more refractory cases 6
- Angioedema without wheals may have several different pathophysiologic mechanisms, and optimal management may involve targeted therapies, such as novel biologics or gene therapy approaches 6