Know Your Blood Parameter: Triiodothyronine (T3)
- Summarised by TGHC Editorial Team
- Jun 23, 2025
- 3 min read
Updated: Dec 22, 2025
Parameter Name
Total T3 (Triiodothyronine)
Total T3, or Triiodothyronine, is one of the key hormones produced by the thyroid gland. It plays a critical role in regulating various physiological processes in the body, including metabolism, heart rate, and body temperature. This hormone is derived from the conversion of thyroxine (T4), another thyroid hormone, and is vital for proper growth and development.
Test Type
Blood
The Total T3 test is performed using a blood sample, typically drawn from a vein in the arm. This test measures the level of Triiodothyronine in the bloodstream, providing valuable insight into thyroid function. Blood tests are a standard method for assessing hormone levels due to their accuracy and reliability.
Normal Range
Adults: 80 – 200 ng/dL
The normal range for Total T3 levels in adults is generally considered to be between 80 and 200 nanograms per deciliter (ng/dL). However, it is important to note that reference ranges can vary slightly between laboratories, and factors such as age, sex, and overall health may influence these values. Therefore, it is essential to interpret results in the context of individual health conditions and laboratory standards.
High Levels Indicate
Hyperthyroidism, thyroiditis, Graves’ disease, or excess thyroid hormone intake.
Elevated levels of Total T3 may suggest hyperthyroidism, a condition where the thyroid gland is overactive, producing excessive amounts of thyroid hormones. This can lead to symptoms such as increased heart rate, weight loss, and anxiety. Other potential causes of high T3 levels include thyroiditis, an inflammation of the thyroid gland, and Graves’ disease, an autoimmune disorder that stimulates the thyroid. Additionally, high T3 levels may result from excessive intake of thyroid hormone medications, which can occur in individuals who are being treated for hypothyroidism.
Low Levels Indicate
Hypothyroidism, starvation, chronic illness, or pituitary dysfunction.
Low Total T3 levels are indicative of hypothyroidism, a condition characterized by an underactive thyroid that fails to produce sufficient hormones. This may lead to symptoms such as fatigue, weight gain, and cold intolerance. Other causes of low T3 levels can include starvation or malnutrition, which can affect hormone production, chronic illnesses that impact metabolic processes, or dysfunction of the pituitary gland, which regulates thyroid hormone secretion.
Why It's Tested
To evaluate thyroid function and diagnose hyperthyroidism or hypothyroidism.
The Total T3 test is conducted to assess thyroid function, helping healthcare providers diagnose conditions such as hyperthyroidism and hypothyroidism. By measuring the levels of T3 alongside other thyroid hormones like TSH (Thyroid Stimulating Hormone) and T4, clinicians can gain a comprehensive understanding of thyroid health and effectively tailor treatment plans for patients.
Associated Symptoms (if abnormal)
High: Anxiety, palpitations, weight loss
Low: Fatigue, cold intolerance, weight gain
When Total T3 levels are abnormal, various symptoms may manifest. High levels can lead to anxiety, increased heart palpitations, significant weight loss, and irritability, reflecting the heightened metabolic state associated with hyperthyroidism. Conversely, low T3 levels may result in symptoms such as persistent fatigue, an increased sensitivity to cold, unexplained weight gain, and even depression, which are typical of an underactive thyroid.
What To Do If Abnormal
Repeat test with TSH and T4; consult endocrinologist if values persist abnormal.
If Total T3 levels are found to be abnormal, it is crucial to conduct follow-up testing, including a Thyroid Stimulating Hormone (TSH) test and a T4 test, to gather more information about thyroid function. If the abnormal values persist, it is advisable to consult with an endocrinologist, a specialist in hormone-related conditions, to determine the underlying cause and appropriate treatment options.
Common Conditions Related
Graves’ disease, Hashimoto’s thyroiditis, thyroid nodules
Several common conditions are associated with abnormal Total T3 levels. Graves’ disease is a prominent cause of hyperthyroidism, while Hashimoto’s thyroiditis is an autoimmune condition that often leads to hypothyroidism. Additionally, the presence of thyroid nodules can affect hormone production and may require further investigation to rule out malignancy or other complications.
Nutrition or Lifestyle Connection
Iodine intake impacts thyroid health; avoid excess soy or goitrogens if hypothyroid.
Nutritional factors play a significant role in thyroid health. Adequate iodine intake is essential for the synthesis of thyroid hormones, and deficiencies can lead to conditions such as goiter or hypothyroidism. Conversely, individuals with hypothyroidism should be cautious with excess consumption of soy products and goitrogens—substances found in certain foods that can inhibit thyroid hormone production. Maintaining a balanced diet rich in essential nutrients is crucial for optimal thyroid function.
References (APA Format)
MedlinePlus. (2023). T3 test.
Mayo Clinic. (2022). Thyroid function tests.
American Thyroid Association. (2023).
