The prevalence of thyroid autoimmunity in patients with urticaria: a systematic review and meta-analysis.

Thyroid autoimmunity is the most common organ-specific autoimmune disorder, which is characterized by the production of thyroid autoantibodies and lymphocytic infiltration into the thyroid. The majority cases of chronic urticaria have unknown (idiopathic) causes, with about 30-40 % possibly having an autoimmune substrate. Considering that autoimmune factors may be the common features of both thyroid autoimmunity and urticaria, it is likely that both entities may coexist within the same patient. A number of studies have investigated the association between thyroid autoimmunity and urticaria. However, most of these studies are relatively small sample size, the power achieved in those studies was not sufficient to detect whether there is an association between urticaria and thyroid autoimmunity. The aim of this study is to combine primary data from all relevant studies to produce reliable estimates of the associations between thyroid autoantibodies and urticaria. Literature databases were searched including Medline, Embase, Web of Science, Chinese Wanfang, and CBM databases from January 1980 to December 2013. A total of 14,203 urticaria cases and 12,339 non-urticaria controls were included in this study. From these data, the odds ratio (OR) with 95% confidence interval (95% CI) was calculated. The meta-analysis results showed that the prevalence of positive thyroid autoantibodies in patients with urticaria was higher than non-urticaria controls (TgAb: OR 6.55, 95% CI 3.19-13.42, P<0.00001, I2=67%; TmAb: OR 4.51, 95% CI 2.78-7.33, P<0.00001, I2=47%; TPOAb: OR 8.71, 95% CI 6.89-11.01, P<0.00001, I2=20%, respectively). The results of this meta-analysis suggested that patients with urticaria were more likely to have thyroid autoimmunity than the control groups.