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Thyroid-Stimulating Hormone (TSH) details

What Thyroid-Stimulating Hormone (TSH) shows

Thyroid-stimulating hormone (TSH) is produced by the pituitary gland and signals your thyroid to produce and release thyroid hormone (T4 and T3), and because of the feedback loop between the pituitary and thyroid, TSH is generally considered the single most sensitive marker for thyroid function โ€” it's the primary screening test used to detect both an underactive thyroid (hypothyroidism, where TSH is typically elevated as the pituitary tries to push a sluggish thyroid harder) and an overactive thyroid (hyperthyroidism, where TSH is typically suppressed low, since the pituitary senses already-excess thyroid hormone). It's also the main test used to guide and adjust thyroid hormone replacement medication dosing.

Higher TSH can point to an underactive thyroid

Often seen with tiredness, feeling cold, weight gain, dry skin, constipation or low mood.

Lower TSH can point to an overactive thyroid

Often seen with a fast heartbeat, feeling hot, anxiety, poor sleep or weight loss.

Who might consider it:

  • Ongoing tiredness, feeling cold, weight changes or thinning hair
  • A family history of thyroid conditions
  • Taking thyroid medication and checking your dose
  • A TSH result outside the range that needs a closer look

What can affect your result

Biotin supplements

High doses can make TSH read falsely low. Pause them before your draw as your lab advises.

Time of day

TSH runs higher in the early morning. Testing at the same time each time keeps results comparable.

Medications

Thyroid medication and some other drugs, such as steroids, shift TSH. After a dose change it takes 6โ€“8 weeks to settle.

Normal ranges

Typical adult range

0.4โ€“4.5 mIU/L

Most labs report a range close to this

Hormunity optimal range

1โ€“2 mIU/L

A narrower functional target

Ranges by sex and age

Group Typical range Good to know
Women, 18+ 0.4โ€“4.5 mIU/L Same range as men. TSH does not differ much by sex.
Men, 18+ 0.4โ€“4.5 mIU/L Same range as women.
Pregnancy Trimester-specific Normally lower, especially in the first trimester. Use the range on your report and your provider's guidance.
Adults 70+ Often slightly higher TSH tends to rise with age. A mildly higher value may be normal for you.

Below 0.4 mIU/L

Considered low. Can be linked to an overactive thyroid, some medications or biotin.

Above 4.5 mIU/L

Considered high. Most often linked to an underactive thyroid.

Each lab sets its own reference range. Always compare your result with the range printed on your report, and review it with a healthcare provider.

Preparation

  • Fasting is not needed.
  • Pause biotin supplements before your draw as your lab or provider advises.
  • If you take thyroid medication, ask your provider whether to take it before or after the draw, and keep that the same each time.
  • Testing in the morning, at about the same time each time, keeps results comparable.

Tests that include Thyroid-Stimulating Hormone (TSH)

Labcorp Not offered
Labcorp Not offered
Quest Not offered
Quest Not offered
Quest Not offered
Quest Not offered
Quest Not offered
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