Fatigue, feeling cold, brain fog, hair thinning, weight that will not budge. These get blamed on stress or getting older all the time. Sometimes they are your thyroid, and thyroid disease is several times more common in women than in men.
TSH is the signal your pituitary gland sends to tell the thyroid to work harder. A high TSH usually means the thyroid is underactive; a low one can mean it is overactive. It is a good screening test, which is why it is the one most often ordered on its own.
Free T4 is the main hormone the thyroid makes, and free T3 is the more active form your body converts it into. Measuring them alongside TSH shows how much hormone is actually circulating, not just how hard your body is asking for it.
Thyroid peroxidase antibodies are a marker of Hashimoto's thyroiditis, the most common cause of an underactive thyroid in the US. They can show up before TSH moves, which is why they are useful when symptoms are there but a basic test came back normal.
A single panel is a snapshot. Illness, some supplements (biotin in particular can distort several thyroid tests), pregnancy, and certain medications all affect the numbers. Results should be reviewed with a licensed provider, who may recommend repeating them before drawing conclusions.
If a TSH-only test did not explain how you feel, a complete thyroid panel is a reasonable next step. You order it online and walk in at Quest Diagnostics on your own schedule.
This guide explains general information and is not medical advice. It doesn't replace a licensed provider reviewing your own history.
