T3 (Triiodothyronine), Total

The T3 (Triiodothyronine), Total test measures the total amount of triiodothyronine hormone in the blood, including both free (active) and bound (inactive) forms. T3 is one of the two main hormones produced by the thyroid gland and plays a critical role in regulating metabolism, heart rate, body temperature, and energy use.

1. What Is T3?

• T3 (triiodothyronine) is a thyroid hormone derived from T4 (thyroxine) and is the more biologically active form.

• Total T3 includes both free T3 (active) and T3 bound to proteins such as thyroxine-binding globulin (TBG).

• T3 levels help assess thyroid gland function and metabolism.

2. Why Is the Total T3 Test Performed?

This test is used to:

• Diagnose hyperthyroidism (overactive thyroid) or assess its severity.

• Help evaluate thyroid function when TSH and T4 results are abnormal or inconclusive.

• Monitor treatment for thyroid disorders.

• Investigate symptoms of thyroid dysfunction such as weight changes, fatigue, or anxiety.

3. T3 Total Reference Range

• Normal range: 80 – 200 ng/dL (may vary slightly by laboratory)

• Interpretation should be based on accompanying TSH and T4 levels.

4. Interpreting T3 Total Results

🔹 Elevated T3:

• Suggests hyperthyroidism (e.g., Graves’ disease, thyroid nodules).

• Can cause symptoms such as weight loss, rapid heartbeat, irritability, and heat intolerance.

🔹 Low T3:

• May indicate hypothyroidism or non-thyroidal illness (e.g., during acute illness or malnutrition).

• Low T3 may occur even when TSH and T4 are normal (low T3 syndrome).

5. What Can Affect T3 Levels?

• Protein-binding changes (e.g., liver disease, pregnancy, oral contraceptives)

• Certain medications (e.g., steroids, amiodarone, beta-blockers)

• Nutritional status and chronic illness

• Thyroid hormone replacement therapy

6. How Is the Test Performed?

• A blood sample is taken from a vein.

• Fasting is not typically required unless part of a broader panel.

7. When to See a Doctor

🚨 Contact your healthcare provider if you:

• Have symptoms of thyroid imbalance (e.g., fatigue, weight gain/loss, temperature sensitivity).

• Are being treated for thyroid disease and need monitoring.

• Have unexpected changes in metabolism, mood, or heart rate.

🔹 Key Takeaways

✅ Total T3 helps assess overall thyroid hormone status, especially in hyperthyroid conditions.

✅ Abnormal levels should be interpreted alongside TSH and T4.

✅ This test supports diagnosis and monitoring of thyroid dysfunction.