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Background: Autoimmune chronic spontaneous urticaria (aiCSU) comes with high disease activity and poor response to treatment. Recently, elevated levels of IgG anti-thyroid peroxidase (aTPO) and low levels of total IgE were reported to be common in aiCSU. Objective: To investigate how high aTPO and low IgE individually and combined are linked to features of aiCSU, including treatment responses. Methods: We analyzed records of patients with CSU from 2 independent cohorts (n = 1120) for demographic, clinical, and laboratory parameters and treatment responses. Total IgE and aTPO were measured, and 4 markers of aiCSU were analyzed: autologous serum skin test, basophil activation test (BAT), and blood eosinophil and basophil counts. Cutoff values were greater than or equal to 34 kU/L (high aTPO) and less than 40 IU/mL (low total IgE). Results: One of 10 patients with CSU had both high aTPO and low IgE (aTPOUPIgEDN, 11%, n = 123). aTPOUPIgEDN was linked to higher age at CSU onset, being female, angioedema, and shorter CSU duration. aTPOUPIgEDN was associated with markers of aiCSU, that is, BAT and autologous serum skin test positivity, basopenia, and eosinopenia (P < .01 for all). Almost half the patients with aTPOUPIgEDN (44%, 19 of 43) had a positive BAT result, the best single marker for aiCSU, versus 12% (43 of 344) of patients without aTPOUPIgEDN (P < .001). Relative risk of showing BAT positivity for a patient with aTPOUPIgEDN is 3.636 (95% CI, 2.382-5.551). Patients with aTPOUPIgEDN showed low response rates to antihistamine treatment as compared with patients without aTPOUPIgEDN (30% vs 47%; P = .01). Conclusions: Our findings suggest that aTPOUPIgEDN is a useful diagnostic marker for aiCSU in everyday clinical practice. |
