Thyroid Stimulating Hormone (TSH)

What is TSH?

Thyroid Stimulating Hormone (TSH) is produced by the pituitary gland and regulates thyroid hormone production. TSH acts as the body’s thermostat for metabolism, rising when thyroid hormones are low and falling when they’re high.

Why is it Tested?

Doctors order TSH as the primary screening test for thyroid disorders because it’s the most sensitive indicator of thyroid function. It’s used to diagnose hyperthyroidism, hypothyroidism, and monitor thyroid hormone replacement therapy.

Normal Ranges

Reference ranges for TSH:

Normal: 0.4–4.0 mIU/L

Some experts suggest optimal TSH levels are between 1.0–2.0 mIU/L, especially for symptom relief and fertility.

Reference ranges vary by authority. Track yours across multiple standards with automatic unit conversions in LabsVault.

What do Abnormal Results Mean?

Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.

Low TSH

Suppressed TSH typically indicates:

Hyperthyroidism (overactive thyroid)
Excessive thyroid hormone medication
Pituitary disorders
Some medications or supplements

High TSH

Elevated TSH suggests:

Hypothyroidism (underactive thyroid)
Pituitary adenoma (rare)
Insufficient thyroid hormone medication
Subclinical hypothyroidism (mild elevation)

How to Track Over Time

TSH levels can fluctuate with stress, illness, medications, and time of day. When monitoring thyroid treatment, TSH changes lag behind dose adjustments by 6–8 weeks. Tracking trends helps optimize medication dosing and detect developing thyroid dysfunction.

Thyroid Stimulating Hormone