Association of Anti-Thyroglobulin and Anti-Thyroid Peroxidase Antibodies in Patients with Primary Hypothyroidism

Background: Hypothyroidism is one of the most important thyroid disorders, and chronic autoimmune (Hashimoto’s) thyroiditis is the most common cause in iodine-replete areas. Anti-thyroglobulin antibodies (anti-Tg Ab) and anti-thyroid peroxidase antibodies (anti-TPO Ab) are commonly associated with the development of chronic autoimmune thyroiditis. However, the precise relationship between them has not been defined yet. Objectives: To study the relationship between anti-Tg Ab and anti-TPO Ab among patients with primary hypothyroidism. Materials and methods: In a cross-sectional study of 169 patients with primary hypothyroidism, their anti-TPO Ab and anti-Tg Ab were measured, analyzed, and correlated together. Results: Positive anti-TPO Ab and anti-Tg Ab were observed in 52.1% of the patients, while 26% and 8.9% of them were only positive for anti-TPO Ab or anti-Tg Ab, respectively, and the remaining 13% showed no positivity for both of them. Anti-Tg Ab titer increased steadily with advancing age in contrast to anti-TPO Ab (P-value = 0.009). The best and highest positive predictive value for having a positive anti-TPO Ab was 91%, and this was obtained at an anti-Tg titer of > 691 IU/mL with a sensitivity of 31% and specificity of 89% at an odds ratio of 3.72 (P-value = 0.014). The best negative predictive value was seen at an anti-Tg Ab titer < 11 IU/mL with a sensitivity of 99% and a specificity of 24% (P-value < 0.001), while a maximum Youden’s value of 1.4 (i.e., maximum sensitivity at a maximum specificity) was obtained at a titer of 26 IU/mL with a positive predictive value of 86% and a negative predictive value of 59% with a sensitivity of 90% and a specificity of 51% (P-value < 0.001). Conclusion: Both anti-Tg Ab and anti-TPO Ab had considerable information in patients with chronic autoimmune hypothyroidism. Anti-Tg Ab tends to be more informative in older people ( > 50 years), where it is more prevalent than anti-TPO Ab. At an anti-Tg Ab titer > 691 IU/mL, we most likely will have positive anti-TPO Ab, while at an anti-Tg Ab titer < 11 IU/ml, we most likely have negative anti-TPO Ab.