Why is my T3 value too high?

In case of hyperthyroidism, the thyroid gland produces too many hormones. There are several causes for hyperthyroidism and a correspondingly high T3 level. In about 95% of cases, the autoimmune disease Graves’ disease or a thyroid autonomy is the underlying cause of hyperthyroidism.

In Graves’ disease, the immune system forms antibodies against the thyroid gland, which take over the place of the hormone TSH on the outside of the cells. The thyroid cells mistakenly believe the antibodies to be TSH and are stimulated to produce hormones. This is why there is far too much T3 and T4 in the blood in Graves’ disease.

If thyroid autonomy is the cause of the hyperthyroidism, there are areas in the thyroid gland itself, for example nodules, which produce hormones in an uncontrolled manner. Often, iodine deficiency is the cause of this and the body tries to compensate for the deficiency through growth. Other causes of hyperthyroidism can be an inflammation of the thyroid gland, tumors or medication.

Why is my T3 value too low?

If the thyroid gland is underactive (hypothyroidism), the thyroid gland produces fewer hormones than the body needs. The thyroid hormones T3 and T4 are too low in the blood. The causes of hypofunction can be problems in the thyroid gland or in hormone-producing structures of the brain, the so-called hypothalamus or the pituitary gland.

A congenital hypofunction of the thyroid gland is rare, occurring in about one in 4,000 children. Also rare is a diet low in iodine as a cause of low T3 levels. A possible cause of hypothyroidism is chronic thyroiditis, Hashimoto’s thyroiditis.

In this autoimmune disease, antibodies are formed against the organ, which partially destroy the tissue. Over time, the thyroid gland in Hashimoto’s thyroiditis develops hypothyroidism and T3 decreases. Diseases of the pituitary gland or hypothalamus due to a tumor can also lead to hypothyroidism.

How does T3 change during pregnancy?

The thyroid hormones have an influence on fertility, the course of pregnancy and the development of the child. The normal values for the hormones change during the pregnancy phases, i.e. differently from trimester to trimester. In addition, up to 15% of all pregnancies have changes in thyroid function, i.e. either overactive or underactive.These disorders can lead to avoidable complications of pregnancy and child development. According to a recent study, the reference values for free T3 are 2.5 – 3.9 pg/ml in the first trimester of pregnancy, 2.1 – 3.6 pg/ml in the second trimester and 2.0 – 3.3 pg/ml in the third trimester (study: Lazarus J et al. , 2014, Eur Thyroid J Guidelines 3: 76-94).