Most patients with the acute onset of hives do not require laboratory evaluation. Those patients with chronic urticaria need evaluation. A skin biopsy is sometimes performed on hives lasting longer than 24 hours. This is to rule out a rare disease called urticarial vasculitis that looks like hives but is really caused by inflammation of blood vessels. Typical screening tests include a complete blood count, liver function tests, thyroid function tests, thyroid antibody tests, and anti-nuclear antibody testing for lupus. Patient’s with angioedema that recurs have determinations of various complement levels and function tests. Order serum C4 and quantitative and qualitative assays of C1-INH. Consider referral to an allergist for skin prick and allergy specific IgE antibody tests.

Dermagraphism. Rub the skin of all patients who complain of hives or itching. If the skin welts up in a few minutes the diagnosis of dermagraphism has been confirmed and no further testing is necessary. These patients are well controlled with antihistamines.