TPO and rheumatoid arthritis: In addition, levels of auto-antibodies (i.e., anti-TPO and anti-Tg), which are considered more reliable in defining auto-immune TGDs, are known to be expressed in other medical conditions that are not related to thyroid diseases, such as asthma, idiopathic urticaria, rheumatoid arthritis, diabetes mellitus type 1 and others [22].