Get tested with Superpower

If you’ve been postponing blood testing for years or feel frustrated by doctor appointments and limited lab panels, you are not alone. Standard healthcare is often reactive, focusing on testing only after symptoms appear or leaving patients in the dark.

Superpower flips that approach. We give you full insight into your body with over 100 biomarkers, personalized action plans, long-term tracking, and answers to your questions, so you can stay ahead of any health issues.

With physician-reviewed results, CLIA-certified labs, and the option for at-home blood draws, Superpower is designed for people who want clarity, convenience, and real accountability - all in one place.

Key benefits of T3 Uptake testing

• Clarifies whether thyroid hormone levels reflect true thyroid function or binding protein changes.
• Helps distinguish real thyroid disease from shifts caused by pregnancy or medications.
• Guides accurate diagnosis when total T4 or T3 results seem inconsistent with symptoms.
• Supports calculation of Free Thyroxine Index to estimate active hormone availability.
• Flags protein abnormalities that may affect how your body transports thyroid hormones.
• Tracks treatment response when thyroid hormone replacement or suppression therapy is adjusted.
• Best interpreted alongside total T4, TSH, and your clinical symptoms for complete clarity.

What is T3 Uptake?

T3 uptake is not a direct measurement of thyroid hormone. Instead, it's an indirect test that estimates how much binding protein is available in your blood to carry thyroid hormones.

Most thyroid hormone in your bloodstream travels attached to carrier proteins, mainly thyroxine-binding globulin (TBG). Only a tiny fraction floats free and active. The T3 uptake test uses a lab technique that mimics this binding competition. It tells us whether you have more or fewer binding sites available than usual.

It reveals the carrier, not the cargo

When binding protein levels are high, the uptake value is low because there are plenty of open seats for hormones. When binding proteins are scarce, the uptake is high because fewer seats are available. This information helps interpret total thyroid hormone levels, distinguishing between true thyroid dysfunction and changes caused simply by shifts in carrier protein amounts.

A supporting actor in thyroid testing

T3 uptake is rarely ordered alone. It's typically combined with total T4 to calculate the free thyroxine index, offering a clearer picture of thyroid function when direct free hormone tests aren't available.

Why is T3 Uptake important?

T3 Uptake measures the binding capacity of proteins in your blood that carry thyroid hormones, particularly thyroid-binding globulin (TBG). It doesn't measure thyroid hormone levels directly but reveals how much "parking space" is available for hormones to attach to carrier proteins. This matters because only unbound, free thyroid hormone can enter cells and regulate metabolism, energy production, heart rate, and body temperature.

When binding proteins are scarce

When T3 Uptake is elevated, it typically means fewer carrier proteins are available, often seen in protein-losing conditions like kidney disease or malnutrition. It can also rise when thyroid hormone levels are high, saturating available binding sites. Women taking estrogen or birth control pills, or during pregnancy, may show falsely low T3 Uptake because estrogen increases TBG production.

When binding capacity is abundant

Lower T3 Uptake suggests an abundance of binding proteins, commonly seen in hypothyroidism, pregnancy, or with estrogen therapy. It can also occur in liver disease or genetic conditions that increase TBG. This doesn't always mean thyroid dysfunction exists - it reflects the transport system, not hormone activity at the tissue level.

The bigger metabolic picture

T3 Uptake is most valuable when paired with total T4 to calculate the Free Thyroxine Index, helping distinguish true thyroid disease from changes in binding proteins. Understanding this distinction prevents misdiagnosis and guides whether symptoms like fatigue or weight changes stem from thyroid function or protein abnormalities affecting hormone transport.

What do my T3 Uptake results mean?

Low T3 uptake values

Low values usually reflect high levels of thyroid hormone binding proteins in the blood, most commonly thyroid binding globulin. When more binding protein is available, less of it gets saturated during the test, resulting in a lower uptake percentage. This pattern is typical during pregnancy, with estrogen therapy, or in certain liver conditions that increase protein production. Low T3 uptake alone does not mean thyroid function is abnormal, but it changes how total thyroid hormone measurements should be interpreted.

Optimal T3 uptake values

Being in range suggests a normal amount of thyroid hormone binding proteins and appropriate binding capacity. This supports accurate interpretation of total thyroid hormone levels and reflects stable protein metabolism. Optimal values typically sit in the mid-range of the reference interval, though individual variation is common and not clinically concerning when thyroid function is otherwise normal.

High T3 uptake values

High values usually reflect low levels of thyroid hormone binding proteins or increased free thyroid hormone that saturates available binding sites. This can occur with low protein states such as severe illness, malnutrition, nephrotic syndrome, or androgen use. It may also appear when thyroid hormone levels are elevated, as in hyperthyroidism. High uptake shifts the interpretation of total hormone measurements upward.

Factors that influence T3 uptake

Pregnancy, oral contraceptives, and hormone replacement therapy commonly lower T3 uptake, while androgens and protein-losing conditions raise it. This test is now less commonly ordered since free thyroid hormone assays provide more direct information.