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Understand where total T4 fits in the thyroid picture.
An early-warning marker for Hashimoto's and related conditions.
A supporting test that clarifies thyroid hormone availability.
See how free T3 reflects the thyroid signal that tissues actually use.
Your primary signal for thyroid control and metabolic pace.
What the free T4 index measures, how it corrects for binding-protein shifts, and when direct free T4 is the more reliable option.
Marker of thyroid autoimmunity that also interferes with thyroglobulin cancer surveillance assays.
Triiodothyronine (T3) is the body’s most active thyroid hormone. It is produced in small amounts by the thyroid gland and largely formed throughout the body when enzymes remove an iodine atom from thyroxine (T4) in organs like the liver and kidneys (peripheral deiodination). Available at 2,000+ lab locations and at-home (select states). See FAQs below
Thyroxine is the primary hormone produced by the thyroid gland in the neck. A total T4 blood test measures the full amount of thyroxine in circulation, combining the small fraction that is unbound with the larger fraction attached to carrier proteins (free and protein‑bound T4). Available at 2,000+ lab locations and at-home (select states). See FAQs below
Thyroid‑stimulating hormone is the body’s main signal that tells the thyroid what to do. It is made by the front part of the pituitary gland at the base of the brain (anterior pituitary) and released into the bloodstream. This hormone is also called thyrotropin (TSH). Available at 2,000+ lab locations and at-home (select states). See FAQs below
Thyroid antibodies are immune proteins in the blood that recognize and attach to parts of the thyroid gland. They are made by B cells when the immune system mistakenly targets the thyroid’s own proteins. The main types are directed against thyroid peroxidase and thyroglobulin, which are enzyme and storage proteins inside the gland, and against the thyroid‑stimulating hormone receptor on thyroid cells (anti‑TPO, anti‑Tg, and TSH receptor antibodies/TRAb). Available at 2,000+ lab locations and at-home (select states). See FAQs below
Thyroid peroxidase antibody testing looks for immune proteins that target a key thyroid enzyme. Thyroid peroxidase lives on the surface of thyroid hormone–making cells and helps attach iodine to the hormone’s building blocks. When the immune system produces antibodies against this enzyme, they circulate in the blood and can be measured. Available at 2,000+ lab locations and at-home (select states). See FAQs below
Thyroglobulin antibody blood testing looks for antibodies your immune system makes against thyroglobulin, the thyroid’s hormone-building protein. Thyroglobulin is produced by thyroid follicular cells and stored in the gland’s colloid; it is the raw material for T4 and T3. When the immune system targets this protein, B cells create thyroglobulin-directed autoantibodies (TgAb, usually IgG). Available at 2,000+ lab locations and at-home (select states). See FAQs below
T3 uptake is a derived measure from a blood sample that estimates the carrying capacity of the blood for thyroid hormones. It does not measure triiodothyronine itself. Instead, it reflects how many binding sites on the blood’s thyroid hormone carrier proteins are available or already occupied. Available at 2,000+ lab locations and at-home (select states). See FAQs below
Free T4 index (FT4I, also called T7) is a calculated estimate of the amount of free thyroxine in your bloodstream. Thyroxine (T4) is a hormone made by the thyroid gland and released into blood mostly attached to carrier proteins (thyroxine‑binding globulin, transthyretin, albumin). Available at 2,000+ lab locations and at-home (select states). See FAQs below
Blood testing detects early thyroid axis slowdown before symptoms. In subclinical hypothyroidism, TSH ↑ with free T4 index N signals pituitary-thyroid feedback strain. At Superpower, we offer these assays with in-clinic and at-home options; home testing is available in selected states. (See FAQs below for more info).
Blood testing clarifies thyroid overactivity before symptoms emerge, protecting cardiovascular and bone systems. At Superpower, we test TSH ↓ with free T4 index N to confirm subclinical hyperthyroidism. We offer in-clinic and at-home testing; home kits are available in selected states. (See FAQs below for more info).
Blood testing clarifies thyroid hormone regulation and immune activity to confirm hypothyroidism. Superpower measures TSH ↑, free T4 index ↓, T4 total ↓, T3 uptake ↓, TPO Ab, and Tg Ab. We offer in‑clinic and at‑home testing; home kits currently available in selected states. (See FAQs below for more info).
Accurate blood testing confirms hyperthyroidism early and clarifies thyroid hormone overactivity and autoimmunity. At Superpower, we test TSH ↓, free T4 index ↑, T4 total ↑, T3 uptake ↑, TPO Ab, and Tg Ab. Superpower offers in-clinic and at-home testing; home blood testing is available in selected states. (See FAQs below for more info).
Blood testing clarifies thyroid autoimmunity and hormone balance in Hashimoto’s, capturing immune antibodies and pituitary-thyroid signaling. Superpower offers TPO Ab, Tg Ab, TSH, and free T4 testing, with in-clinic and at-home options. Home testing for Hashimoto’s is currently available in selected states. (See FAQs below for more info).
Accurate blood testing confirms Graves’ disease by showing thyroid overactivity and autoimmune activity. At Superpower, we test TSH, free T4, TPO Ab, and Tg Ab. We offer in-clinic and at-home testing; home collection is available in selected states. (See FAQs below for more info).
Your TSH test reveals whether your thyroid is working too hard, too little, or just right, but the numbers tell a more complex story than most doctors explain.
Your thyroid controls metabolism, energy, and dozens of body functions, but standard testing often misses the full story.
Your TPO antibody results may reveal whether your immune system is attacking your thyroid, but understanding the range chart requires more context than most biomarker test reports provide.
Your TSH levels reveal how well your thyroid and brain communicate, but "normal" doesn't always mean optimal for you.
Free T4 measures the active form of your thyroid hormone that reaches your cells and drives metabolism.
Free T3 measures the active hormone driving your metabolism, while total T3 includes both active and inactive forms.
Your free T3 levels reveal how well your body converts and uses the most active thyroid hormone.
Cold sensitivity that goes beyond personal preference often has an identifiable biological cause. This guide covers the most common reasons and what to look for on bloodwork.
Intense cold sensitivity, particularly when others around you are comfortable, often has a biological explanation that blood testing can clarify.
Persistent cold sensitivity often traces to thyroid, iron, or blood sugar patterns — and most are identifiable through standard bloodwork.
Unexplained cold sensitivity is rarely random. Several well-documented biological causes are identifiable through standard blood testing.
Persistent cold sensitivity is often traceable to measurable biological causes. Here is what your bloodwork may reveal.
Eight documented reasons you might always feel cold, with the biomarkers that can help identify what's driving it.
Why some people feel colder than those around them — and the biomarkers most commonly behind the difference.
A practical guide to the biological causes of persistent cold sensitivity, with the biomarkers most worth testing.
Persistent cold sensitivity often has a biological explanation. This guide covers the hormonal, hematological, and metabolic causes most commonly found on bloodwork.
Eight clinically documented causes of persistent cold sensitivity, each paired with the biomarkers used to identify them through standard blood testing.
What it means to feel cold all the time, the conditions most likely behind it, and when to seek clinical evaluation.
A clinical guide to the most common causes of cold intolerance and the biomarkers that help explain it.
A concise guide to why you might always feel cold and which biomarkers are most likely to explain it.
