TSH (Thyroid Stimulating Hormone): normal range & what your result means

Q: Why does high TSH mean an underactive thyroid?

When the thyroid makes too little hormone, the pituitary raises TSH to push it harder — so a high TSH signals an underactive gland, not an overactive one.

Q: What is subclinical hypothyroidism?

A mildly raised TSH with normal T4 and few or no symptoms. It is monitored and sometimes treated, depending on the level and your situation.

TSH is the pituitary’s signal to the thyroid and the single best screening test for thyroid problems. It moves opposite to thyroid activity.

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Typical adult reference range

Measure	Range
Normal	0.4–4.0 mIU/L
High	> 4.0 mIU/L (underactive thyroid)
Low	< 0.4 mIU/L (overactive thyroid)

What a HIGH result can mean

High TSH means an UNDER-active thyroid (hypothyroidism): tiredness, weight gain, feeling cold, dry skin

What a LOW result can mean

Low TSH means an OVER-active thyroid (hyperthyroidism): weight loss, palpitations, anxiety, heat intolerance

Ranges vary by lab. Reference ranges are TYPICAL ADULT values and vary by laboratory, age, sex, pregnancy and the method used. Always read your result against the range printed on YOUR report, and let your doctor interpret it alongside your history.

Frequently asked questions

Why does high TSH mean an underactive thyroid?

When the thyroid makes too little hormone, the pituitary raises TSH to push it harder — so a high TSH signals an underactive gland, not an overactive one.

What is subclinical hypothyroidism?

A mildly raised TSH with normal T4 and few or no symptoms. It is monitored and sometimes treated, depending on the level and your situation.

Upload your report to MedDroid →

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MedDroid is an AI medical assistant and can make mistakes. It provides general health information, not a diagnosis or medical advice — always consult a qualified clinician. In an emergency, contact your local emergency number immediately.