A full thyroid read is more than one number: TSH, free T4, and free T3. TSH tells your physician how hard your brain is signaling the thyroid; free T4 and free T3 show how much usable hormone is actually circulating. Read together, they explain why someone can feel hypothyroid symptoms while a lone TSH looks “fine.”
TSH: the signal, not the hormone
TSH (thyroid stimulating hormone) is not a thyroid hormone at all. It is the message your pituitary sends to tell the thyroid to work. A high TSH usually means the brain is signaling harder because hormone is low; a low TSH can mean the opposite. Many providers still stop at TSH, and many labs flag anything under about 4.0 mIU/L as normal, while some clinicians read a narrower optimal band closer to 0.3 to 3.0. That gap between “normal” and “optimal” is where a lot of unexplained fatigue lives.
Free T4 and free T3: the hormone you can use
Free T4 is largely a storage form; your body converts it into free T3, the active hormone your cells actually run on. A TSH and free T4 that look acceptable can still sit over a low free T3 if that conversion is sluggish, which a TSH-only check never shows. This is why free T3 is worth measuring rather than assuming. The word “free” matters too: it is the unbound fraction available to tissues, not the portion locked to carrier proteins.
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Antibodies and reverse T3: the context markers
When the thyroid picture is unclear, a physician may look wider: TPO and thyroglobulin antibodies, which point to an autoimmune pattern, and reverse T3. These do not replace TSH, free T4, and free T3; they add context to them. The point is the same across the panel: one marker rarely settles the question, and the pattern is what a clinician reads.
Thyroid or perimenopause? Why the overlap matters
Fatigue, brain fog, weight changes, mood shifts, poor sleep, hair thinning, and feeling cold all appear on the thyroid list and the perimenopause list. That overlap is exactly why women in their 40s are so often told it is “just hormones” when the thyroid was never fully measured, or told it is thyroid when estradiol and progesterone are shifting too. The only way to separate them is to measure both, in the same panel, and read them together. (See perimenopause by the markers and HRT options in perimenopause.)
What your physician does with a thyroid panel (labs before molecules)
At Telos, the information you share and the panel you complete are reviewed by a licensed physician through the affiliated medical group. They read TSH, free T4, and free T3 together, against your symptoms and the rest of your markers, and decide what, if anything, fits. The core hormone and health panel exists so the thyroid story is read in context, next to your sex hormones and metabolic markers, rather than from a single flagged value. This is the “labs before molecules” idea: measure enough to see the real pattern first. Nothing here is medical advice. (See what a full panel covers.)