Total T3: What Your Results Mean
Bottom line: Total T3 includes bound and free T3. Normal varies by lab. Used alongside TSH and Free T4 to evaluate thyroid function.
What Is Total T3?
Total T3, or total triiodothyronine, is a blood test that measures the amount of the thyroid hormone triiodothyronine (T3) that is circulating in your bloodstream. T3 is one of the two primary hormones produced by your thyroid gland, the other being thyroxine (T4). A significant portion of the T3 in your blood is bound to proteins, such as thyroxine-binding globulin (TBG), albumin, and prealbumin. Total T3 includes both the T3 that is bound to these proteins and the small amount that is free and biologically active.
The thyroid hormones T3 and T4 are crucial for regulating your body's metabolism – the process by which your body converts food into energy. They influence numerous bodily functions, including heart rate, body temperature, digestion, and brain development. While free T3 is the form that actively affects your cells, measuring total T3 provides a comprehensive picture of thyroid hormone status, especially when considered alongside other thyroid function tests. Levels of total T3 can indicate whether your thyroid gland is overactive (hyperthyroidism) or underactive (hypothyroidism), or if there are issues with the proteins that bind these hormones.
Total T3 Reference Ranges
| Classification | Range (ng/dL) |
|---|---|
| Very Low | 0.4 - 0.8 |
| Low | 0.9 - 1.2 |
| Normal | 1.3 - 2.3 |
| High | 2.4 - 3.0 |
| Very High | 3.1 - 4.5 |
What Affects Your Total T3 Levels?
- Pregnancy
- Certain medications (e.g., oral contraceptives, androgens, anabolic steroids)
- Liver disease
- Kidney disease
- Severe illness or trauma
- Malnutrition or fasting
- Thyroid hormone replacement therapy
- High levels of binding proteins
When to Get Tested
A Total T3 test is typically ordered as part of a broader thyroid function evaluation, especially when a doctor suspects a thyroid disorder based on symptoms. Symptoms of an overactive thyroid (hyperthyroidism) might include unexplained weight loss, rapid heartbeat, anxiety, and tremors, while symptoms of an underactive thyroid (hypothyroidism) can involve fatigue, weight gain, feeling cold, and depression. This test helps to assess the overall amount of thyroid hormone activity in the body and can aid in diagnosing conditions like hyperthyroidism or monitoring the effectiveness of treatment for thyroid diseases.
Look Up Your Total T3 Result
Select your value below to see a detailed breakdown of what it means:
Read the Full Blood Test Guide
Frequently Asked Questions
Yes, pregnancy can significantly influence Total T3 levels. Levels tend to increase during pregnancy due to changes in the binding proteins that carry thyroid hormones. This is a normal physiological adaptation.
If your Total T3 is high and your Thyroid Stimulating Hormone (TSH) is normal, it could suggest a condition called toxic multinodular goiter or toxic adenoma, where nodules in the thyroid gland are overproducing thyroid hormone independently of TSH stimulation. It's important to discuss these results with your doctor for proper diagnosis.
Certain medications can interfere with Total T3 levels. For example, estrogen-containing medications can increase levels by boosting binding proteins, while androgens or anabolic steroids can decrease them by reducing binding proteins. Always inform your doctor about all medications you are taking.