Abstract

Background: Epidemiological studies showed that the population has a high immune disease prevalence, and thyroid immune diseases are among the top autoimmune disorders seen in clinical practice. Investigators noticed an association between some non-thyroidal conditions with thyroid autoantibodies, and some of the outcomes of these non–thyroid diseases may be affected by the presence of these thyroid antibodies.

Objective: To investigate the association of thyroid autoantibodies with non-thyroidal diseases and their clinical significance, such as the positive or negative impact on the disease outcome.

Methods: A systematic literature review was done using selection criteria with the help of search questions. Multiple search engines were searched for eligible articles. Articles were filtered based on the inclusion and exclusion criteria. Data were extracted and analysed for clinical or statistical significance between case and control groups in selected studies.

Results: Eighteen (18) articles fulfilled the inclusion and exclusion criteria; 44.4% were analytical cross-section studies, 5% were prospective studies, 5.5% were meta-analysis studies, 5.5% were case-control studies, and 16.7% were retrospective studies. The included studies aimed to find an association between TPO-Ab, TG-Ab, and some non-thyroidal diseases such as Vitamin D deficiency, Allergic diseases, mood disorders, women’s reproductive system diseases, abortion, systemic lupus erythematosus, rheumatoid disease, Celiac disease, Type 1 diabetes, and breast cancer. The ORs in the included studies were > 1, and the confidence intervals did not cross 1, which means both clinical (favour positivity in case groups) and statistical (existing difference between case and control groups) significance. The “I^2 value”, which is an indicator for heterogeneity of the studies included in the meta-analysis, was high in the included research (>50%), which indicates heterogeneity of the included study. TPO-Ab was a favourable prognostic indicator in cases of breast cancer. Relative risk (RR) was used to assess the disease-free survival rate in subjects with breast carcinoma. The survival rate between patients with TPO-Ab > 0.3u/ml and <0.3u/ml was statistically significant (P value 0.016), and relative risk = 3.46.

Conclusion: Thyroid autoantibodies are not exclusively markers of thyroid autoimmune diseases but can also be markers and indicators of non-thyroidal illnesses. Their presence could be either a favourable prognostic indicator, as with breast carcinoma cases or unfavourable prognostic indicator, as with abortion. Further studies are recommended to explore more associations.

Key words: Thyroid, thyroid autoantibodies, thyroid diseases, non-thyroidal diseases.