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Marker · Educational ranges, not diagnosis

TSH and free T4

Also called thyroid stimulating hormone, thyroxine.

TSH is the pituitary signal that tells the thyroid to work. Free T4 is the unbound thyroxine in blood. Together they are the usual first thyroid panel.

Read this first

  • Coach, not doctor. Aaron Cuha is a coach, not a doctor. No clinical credential is claimed for him, or for these pages. A number on a panel is a conversation starter with a clinician, not a DIY diagnosis. Nothing here is a prescription, a protocol, or a reason to start or stop a medicine. Educational use only. This database summarizes published research and is not medical advice. Where a dose appears it is a record of what a trial or clinic ran, or what people describe doing, with its source attached. Nothing here is a recommendation for personal use.
  • Affiliate disclosure. Knowledge stays free. Every page, every guide and every tool is free to read and stays free. Lab-panel affiliate links, when they exist, live on /bloodwork/partners and print what is earned on the row, or that nothing is earned today. This glossary does not sell panels. The Archive does not order labs.
  • Three lab stories stay separate. /bloodwork is the human panel. /testing and /prices/labs are peptide certificate chemistry. /supplements/quality is what is in the bottle.

Why a longevity audience asks

Selenium and iodine sit next to thyroid function in the supplement aisle, and both can make autoimmune thyroid disease worse if they are stacked casually. This page is a map to a clinician, not a Hashimoto protocol.

How a coach reads it

Labs often use a TSH interval around 0.4 to 4.0 mIU/L, and some clinicians talk about a tighter band in specific settings. Free T4 has its own interval. This site will not assign you a thyroid diagnosis or a desiccated-thyroid stack. High TSH with low free T4 is a different conversation from high TSH with normal free T4.

Units on this page: mIU/L, ng/dL

When it is low

Low TSH can mean over-replacement, a hyperthyroid state, or a pituitary problem. Stop DIY thyroid or iodine and get help.

When it is high

High TSH is a reason to look at free T4, sometimes free T3, and antibodies if the clinician wants them. It is not a reason to buy selenium and iodine together because a forum said to.

Easy ways to misread it

  • Biotin interferes with some TSH and free-T4 immunoassays.
  • Do not start iodine if you have known Hashimoto's without a clinician.
  • Free T3 is optional and easy to over-read.

What to ask a clinician

Ask for TSH and free T4. Ask whether antibodies are useful. Tell the lab about biotin. Do not add iodine on your own.

Related supplements

Conversation ranges on this entry are named as clinician or owner ranges, not as a trial result invented for the page. Related compound pages carry the trial record.