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 Thyroxine (T4), Total testing

• Measures your thyroid's main hormone output to assess gland function.
• Spots overactive or underactive thyroid before symptoms become severe.
• Explains fatigue, weight changes, mood shifts, or temperature sensitivity.
• Guides medication dosing if you're on thyroid hormone replacement therapy.
• Flags thyroid imbalance that may affect menstrual cycles or fertility.
• Tracks thyroid stability during pregnancy to protect maternal and fetal health.
• Best interpreted with TSH and your symptoms for complete thyroid assessment.

What is Thyroxine (T4), Total?

Total thyroxine (T4) is the primary hormone produced by your thyroid gland, a small butterfly-shaped organ at the base of your neck. The thyroid manufactures T4 by combining iodine with the amino acid tyrosine, then releases it into your bloodstream. "Total" T4 refers to all the T4 circulating in your blood, both the portion bound to carrier proteins and the small free fraction that is biologically active.

T4 is your body's metabolic messenger

T4 acts as a master regulator of metabolism, influencing how fast your cells burn energy, generate heat, and carry out essential functions. Although T4 itself is relatively inactive, tissues throughout your body convert it into triiodothyronine (T3), the more potent form that directly controls metabolic rate.

It reflects thyroid gland output

Measuring total T4 provides a snapshot of how much hormone your thyroid is producing and releasing. It serves as a key indicator of thyroid function, helping to reveal whether your gland is working normally, underperforming, or overactive.

Why is Thyroxine (T4), Total important?

Total T4 measures the primary hormone your thyroid gland releases into circulation, serving as a direct window into whether your thyroid is producing enough raw material to fuel metabolism, energy production, and cellular function throughout your body. It reflects the combined pool of bound and unbound hormone before tissues convert it to the more active T3. When total T4 sits within the typical reference range, your thyroid is generally keeping pace with your body's demands.

When your thyroid underproduces hormone

Values below the normal range signal hypothyroidism, meaning your cells receive insufficient thyroid hormone to maintain normal metabolic rate. You may experience fatigue, weight gain, cold intolerance, constipation, dry skin, and slowed thinking. In women, low T4 can disrupt menstrual cycles and fertility, while in children it may impair growth and cognitive development.

When your thyroid releases too much

Elevated total T4 points toward hyperthyroidism, where excess hormone accelerates metabolism beyond healthy limits. This drives symptoms like anxiety, tremor, heat intolerance, weight loss, rapid heartbeat, and diarrhea. Women may notice lighter or absent periods, and prolonged elevation stresses the heart and bones.

The metabolic command center

Total T4 connects thyroid function to cardiovascular health, bone density, reproductive cycles, and mental clarity. Persistent imbalances increase risk for heart arrhythmias, osteoporosis, and metabolic disorders over time, making this biomarker essential for understanding your body's energy regulation at its source.

What do my Thyroxine (T4), Total results mean?

Low total T4 levels

Low values usually reflect reduced thyroid hormone production or impaired thyroid gland function, a state called hypothyroidism. This can slow metabolism, reduce energy production in cells, and affect nearly every organ system. Common effects include fatigue, cold sensitivity, weight gain, dry skin, and slowed heart rate. In pregnancy, low T4 can impair fetal brain development. Causes include autoimmune thyroid disease, iodine deficiency, pituitary dysfunction, or certain medications.

Optimal total T4 levels

Being in range suggests your thyroid gland is producing adequate thyroxine and your binding proteins are functioning normally. This supports stable metabolic rate, energy production, and cellular function throughout the body. Most healthy adults sit in the mid to upper portion of the reference range, though individual optimal levels vary.

High total T4 levels

High values usually reflect excess thyroid hormone production, known as hyperthyroidism, or increased thyroid-binding proteins. Hyperthyroidism accelerates metabolism, increases heart rate, and can cause anxiety, weight loss, heat intolerance, and tremor. Elevated binding proteins, common in pregnancy or with estrogen use, raise total T4 without causing symptoms. Graves' disease, toxic nodules, and thyroiditis are frequent causes of true hormone excess.

Factors that influence total T4

Total T4 measures both bound and free hormone, so it rises with increased binding proteins during pregnancy, estrogen therapy, or certain liver conditions, even when active hormone is normal. Severe illness, malnutrition, and some medications lower binding proteins and total T4. Free T4 testing often clarifies the clinical picture.