The article discusses the clinical significance of thyroid antibodies and their relevance in diagnosing and managing thyroid disorders, offering insights into when and why these tests are used. It also addresses specific clinical cases involving thyroid antibodies.

Case 1: A 30-year-old female with k/c/o autoimmune hypothyroidism on thyroxine 50 mcg for the last 2 years presented to the clinic with no fresh complaints except her latest thyroid antibodies (Anti TPO) titer was elevated when compared to her previous report, her thyroid function test (TFT) was within normal range. Should we increase the dose of Levothyroxine (LT4) or start her on steroids in view of her latest reports?

Case 2: A 25-year-old female patient with a history of amenorrhea for 1 year, her hormonal profile including thyroid profile was ordered along with anti-TPO, the Thyroid profile showed normal TSH (4 mU/L), normal FT4, and he Anti- TPO was positive. Should we start the patient on Levothyroxine (LT4) treatment based on these reports?

Thyroid antibodies and their significance

Thyroid antibodies develop in an individual when the immune system mistakenly targets components of the thyroid gland. These antibodies appear to be a secondary response to thyroid injury and are not thought to cause disease themselves, although they may contribute to its development and chronicity. This autoimmune response can cause chronic thyroid inflammation, thyroid function disruption, and tissue damage.

These antibodies are responsible for causing autoimmune thyroid disorders such as Hashimoto’s thyroiditis and Grave’s disease. These antibodies can cross the placenta barrier and can have a potential effect on the cognitive development of neonates. Euthyroid women with thyroid antibodies have been shown to suffer from increased early pregnancy loss.

There are three main antibodies used in clinical practice:

1. Thyroid peroxidase antibodies (TPO Ab or anti-TPO)
2. Thyroglobulin antibodies (Tg Ab)
3. Thyroid-stimulating hormone receptor antibodies (TSHRAb or TRAb)

These antibodies are usually ordered in cases of subclinical hypothyroidism (High TSH, normal FT4), goitre, hyperthyroidism (not confirmed by clinical presentation or TFT), and monitoring after cancer treatment. Some people will test positive for more than one type of thyroid antibody. Positive antibodies can be present in euthyroid persons.

Thyroid peroxidase antibodies (TPO Ab)

1. TPO antibody helps in confirming the diagnosis of autoimmune hypothyroidism and is found in >90% of the cases.
2. Thyroid peroxidase is an enzyme crucial to producing thyroid hormones, antibodies against TPO may interfere with the action of this enzyme.
3. TPO Ab is raised in Hashimoto’s thyroiditis and sometimes in Grave’s disease. A negative antibody test points out another cause for underlying thyroid disorder.
4. The presence of TPO Ab in patients with subclinical hypothyroidism indicates the person may develop full-blown thyroid disease in the future; such patients should be on regular follow-up.
5. As per guidelines, Levothyroxine treatment can be considered in such patients.

Thyroglobulin antibodies (Tg Ab)

1. Thyroglobulin antibody is used in follow-up of treated thyroid cancer patients. Their presence can affect the accuracy of the measurement of thyroglobulin.
2. Thyroglobulin (Tg) is produced by cancer as well as normal cells, post thyroid surgery or radioactive iodine ablation the thyroglobulin levels should not be detectable in the blood.
3. Thyroglobulin detection or increasing levels points towards the recurrence of the cancer. In the presence of positive Tg Ab in such patients, additional tests should be done to monitor relapses.

Thyroid-stimulating hormone receptor antibodies (TSHRAb or TRAb):

1. TSHR antibody is raised in Grave’s disease.
2. TRAb mimics the thyroid stimulating hormone (TSH) which results in overproduction of thyroid hormones from the thyroid gland.
3. The level of TRAb antibodies often reflects the severity of the disease.
4. TRAb can cross the placenta and can cause fetal thyrotoxicosis which is confirmed by fetal tachycardia, goitre and bone age advancement in pregnancy.

When to repeat thyroid antibodies test?

Thyroid antibodies often remain in the body even after the thyroid disorder has been successfully treated. So it should not be repeated as often as thyroid function tests.

1. Repeat measurement of Anti TPO Ab is rarely useful as their level does not influence the treatment and response to treatment.
2. Repeat measurement of TRAb can be used to guide treatment decisions in Grave’s disease. The relapse is more likely in patients after stopping the antithyroid drug with raised TRAb levels.
3. Repeat measurement of TgAb is useful in the follow-up of thyroid cancer to ensure the accuracy of thyroglobulin measurement.

Disclaimer- The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of M3 India.

About the author of this article: Dr Hitesh Saraogi is a diabetologist, physician and an obesity specialist at Dhanvantari Hospital, Raj Nagar Extension, Ghaziabad.