Thyroid function

TSH test (thyroid-stimulating hormone)

TSH is the signal your brain sends to tell your thyroid how hard to work.

Included in every $199 draw, with Free T3 and Free T4

Key benefits of TSH testing

Screens for underactive and overactive thyroid.
Explains fatigue, weight change, feeling cold, hair loss or anxiety.
Reads best with Free T3 and Free T4, which Insyght includes.
Tracks thyroid medication dosing over time.
Catches early shifts before full symptoms appear.

What is TSH?

TSH is made by the pituitary gland in your brain. When thyroid hormone runs low, TSH rises to push the thyroid harder. When thyroid hormone runs high, TSH drops.

Why TSH matters

Your thyroid sets the pace of your metabolism. Too little hormone slows everything down. Too much speeds up your heart rate and burns through energy.

What your TSH results mean

High TSH: your thyroid may be underactive (hypothyroidism). Common signs are tiredness, weight gain and feeling cold.
In range: your thyroid signaling looks balanced. Check Free T3 and Free T4 too.
Low TSH: your thyroid may be overactive (hyperthyroidism). Common signs are a racing heart, anxiety and weight loss.
Context matters: biotin supplements, illness, pregnancy and some medications can skew thyroid results.

Standard vs. optimal range

	Range
Standard lab range	About 0.4 to 4.5 mIU/L (varies by lab)
Insyght optimal range	Set by the Insyght medical team

LowHigh

Lab reference rangeYour optimal range

A value can read normal on a standard panel and still sit outside optimal. Insyght flags it.

Do I need a TSH test?

Tired no matter how much you sleep, gaining weight without changing habits, or always cold? These are classic thyroid signs, and a simple TSH test is where to start.

Test your thyroid, not just TSH

Insyght measures TSH, Free T3 and Free T4 together, so your physician sees how your thyroid is really working. $199 a year.

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Similar biomarkers

Free T3Free T4Ferritin Cortisol Vitamin D

Frequently asked questions

Do I need to stop biotin before a thyroid test?

Yes. Stop biotin, often found in hair and nail supplements, for 2 to 3 days before your draw. It can falsely skew results.

Can TSH be normal if I still have thyroid symptoms?

Yes. Free T3, Free T4, iron and other factors can explain symptoms. That's why Insyght tests the full set.

How often should I check my thyroid?

Once a year for most people. More often if you take thyroid medication or your results are borderline.

Medically reviewed by Dr. Maria Gutierrez Horn, MD, FACE, Board-certified endocrinologist, in practice since 2001. Last updated September 28, 2026.