Chronic urticaria (more than 6 weeks)

Laboratory tests

• FBC
• CRP
• Total IgE (urticaria resistant to H1 antihistamines, before second-line treatment)if needednon-French guidelineChronic spontaneous urticaria followed in a specialist setting or resistant to H1 antihistamines: low total IgE, with raised anti-TPO, suggest an autoimmune type IIb form ^[2].
• Anti-TPO antibodies (urticaria resistant to H1 antihistamines)if neededChronic spontaneous urticaria resistant to H1 antihistamines (minimum tests of HAS 2003) or followed in a specialist setting (EAACI 2022); if positive, measure TSH ^[2,3].
• TSH (if anti-TPO antibodies positive or signs of thyroid dysfunction)if neededPositive anti-TPO antibodies, or clinical signs of thyroid dysfunction ^[3].
• Antinuclear antibodies, CH50, C3 and C4 (if inflammatory syndrome, abnormal FBC or extracutaneous signs)if neededInflammatory syndrome, FBC abnormality, or guiding clinical signs appearing later (arthralgia, fever, fixed lesions) ^[3].
• Toxocariasis serology (if hypereosinophilia)if neededFBC abnormality (hypereosinophilia) or inflammatory syndrome; toxocariasis is the only parasitosis associated with chronic urticaria in the literature analysed by the 2003 jury ^[3].
• Cryoglobulinsif neededCold urticaria with clinical signs suggesting a cryopathy or systemic disease (purpura, arthralgia, peripheral neuropathy): look for cryoglobulins and cold agglutinins ^[4]; the 2003 conference also cited cryofibrinogenaemia and a monoclonal immunoglobulin ^[3]. Without these signs, after a positive ice cube test, FBC and CRP are enough ^[4].
• serum protein electrophoresis (cold urticaria with purpura, arthralgia, neuropathy or other sign of systemic disease)if neededCold urticaria with clinical signs suggesting a cryopathy or systemic disease (purpura, arthralgia, peripheral neuropathy): look for cryoglobulins and cold agglutinins ^[4]; the 2003 conference also cited cryofibrinogenaemia and a monoclonal immunoglobulin ^[3]. Without these signs, after a positive ice cube test, FBC and CRP are enough ^[4].

Urine tests

• Urine dipstick (if fixed lesions, purpura, arthralgia or fever, to look for renal involvement)if needednon-French guidelineThe British guide (BSACI, 2015) cites the dipstick to detect haematuria and proteinuria (urinary tract infection, kidney involvement of vasculitis); the American Family Physician (2017) counts it among the tests to consider ^[5,6]. Neither the 2026 international recommendation nor the 2003 French conference cites it ^[3,7].

• No laboratory tests: the diagnosis is clinical and the search for a triggering factor relies on the history.