Chronic urticaria (CU) is a common disease in which most cases were considered to be idiopathic. Recent evidence indicates that at least a subset of cases of chronic idiopathic urticaria are autoimmune in origin.

We aimed to characterize the association between CU, autoimmune diseases, and autoimmune/inflammatory serologic markers in a large unselected population.

Data on 12,778 patients given a diagnosis of CU by either allergy or dermatology specialists during 17 years in a large health maintenance organization in Israel were collected. For each patient, we collected information on diagnosis of major, well-defined autoimmune diseases and autoimmunity- and inflammatory-related serologic markers. Similar data were collected for a control group comprised of 10,714 patients who visited dermatologists, family physicians, or allergy specialists and had no indication of CU.

Having CU was associated with an increased odds ratio for hypothyroidism, hyperthyroidism, and antithyroid antibodies. Female patients with CU had a significantly higher incidence of rheumatoid arthritis, Sjögren syndrome, celiac disease, type I diabetes mellitus, and systemic lupus erythematosus, mostly diagnosed during the 10 years after the diagnosis of CU. High mean platelet volume, positive rheumatoid factor, and antinuclear antibodies were all significantly more prevalent in patients with CU.

A strong association was found between CU and major autoimmune diseases. A common pathogenic mechanism is implied by the high prevalence of autoantibodies and the existence of a chronic inflammatory process expressed by the high mean platelet volume. These findings have implications for the diagnosis, management, and prognosis of patients with CU.