Antiphospholipid antibodies in autoimmune thyroid diseases

BACKGROUND: Antiphospholipid (aPL) antibodies have been reported in several autoimmune diseases. The aim of this study was to evaluate the frequency of aPL (anti‐cardiolipin antibodies (aCL) and anti‐β2 glycoprotein I antibodies (aβ2GPI)) in patients with autoimmune thyroid diseases (AITD). METHODS: One hundred and ninety‐five patients with AITD (139 Hashimoto's thyroiditis (HT) patients and 56 Graves' disease (GD) patients) and 90 healthy blood donors (HBD) were studied. IgG, IgA and IgM aCL and aβ2GPI were determined by ELISA. RESULTS: One hundred fifty‐four AITD patients were women and 41 were men. Fifty‐six healthy subjects were women and 34 were men. The median age of patients and the control group was 45 and 38.5 years, respectively. The frequency of aPL was significantly higher in patients with AITD and in patients with HT than in HBD (33.3% vs 11.1%, p < 10(−3) and 38.1% vs 11.1%, p < 10(−3)). The frequency of aPL in GD was significantly lower than in HT (21.4% vs 38.1%, p = 0.025). In patients with HT, aβ2GPI (34.5%) was significantly more frequent than aCL (13.6%) (p < 10(−3)). The frequency of aβ2GPI was significantly higher in patients with HT than in healthy population (34.5% vs 11.1%, p < 10(−3)). In HT patients, IgA isotype of aβ2GPI was significantly more common than in HBD and in GD patients (27.3% vs 7.8%, p < 10(−3) and 27.3% vs 12.5%, p = 0.02, respectively). CONCLUSION: aβ2GPI and not aCL were frequent in AITD. IgA was the predominant isotype of aβ2GPI. aβ2GPI‐IgA was more frequent in HT than in GD.