Marker · Ranges for learning, not a diagnosis
TSH and free T4
Also called thyroid stimulating hormone, thyroxine.
TSH is the signal from a gland in the brain (the pituitary) that tells the thyroid to work. Free T4 is the thyroid hormone floating free in the blood. Together they are the usual first thyroid tests.
Read this first
- Coach, not doctor. Aaron Cuha is a coach, not a doctor. No medical credential is claimed for him, or for these pages. A number on a blood test is something to talk over with a doctor, not something to diagnose yourself with. Nothing here is a prescription, a plan to follow, 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.
- Knowledge stays free. Knowledge stays free. Every page, every guide and every tool is free to read and stays free. No partner paid for a place on these pages.
- Three kinds of lab page, kept apart. /bloodwork is blood tests for people. /testing and /prices/labs are lab tests on peptide vials. /supplements/quality is what is in the bottle.
Why a longevity audience asks
Selenium and iodine get sold for the thyroid, and both can make thyroid disease where the body attacks the thyroid worse if they are taken carelessly. This page points you to a doctor. It is not a Hashimoto's plan.
How a coach reads it
Labs often use a TSH range of about 0.4 to 4.0 mIU/L, and some doctors use a tighter range in certain cases. Free T4 has its own range. This site will not give you a thyroid diagnosis or a dried thyroid gland stack. High TSH with low free T4 means something different from high TSH with normal free T4. This is not a diagnosis.
Units on this page: mIU/L, ng/dL
When it is low
Low TSH can mean too much thyroid medicine, an overactive thyroid, or a pituitary problem. Stop any do-it-yourself 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 your doctor wants them. It is not a reason to buy selenium and iodine together because a forum said to.
Easy ways to misread it
- Biotin throws off some TSH and free T4 lab tests.
- If you have Hashimoto's, do not start iodine without a doctor.
- Free T3 is optional and easy to read too much into.
What to ask your doctor
Ask for TSH and free T4. Ask whether antibody tests are useful. Tell the lab about biotin. Do not add iodine on your own.
Related supplements
The ranges on this page are labeled as a doctor's ranges or the owner's. They are not a trial result made up for the page. The related compound pages show the trials.