TSH (Thyroid Stimulating Hormone)
TSH is produced by the pituitary gland in the brain and controls the thyroid gland. When thyroid hormones (T3 and T4) are low, the pituitary releases more TSH to stimulate the thyroid — like turning up a thermostat. When thyroid hormones are high, TSH drops. This makes TSH the single most useful screening test for thyroid disorders.
Reference Ranges
Male
0.4 – 4
mIU/L
Female
0.4 – 4
mIU/L
Child
0.7 – 6
mIU/L
Ages 1–12, varies by age
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
Low TSH (below 0.4) suggests hyperthyroidism — the thyroid is overactive and producing too much hormone, so the pituitary backs off. Symptoms include weight loss, rapid heartbeat, anxiety, tremors, heat intolerance, and diarrhea. Graves' disease is the most common cause.
What High Levels Mean
High TSH (above 4.0) suggests hypothyroidism — the thyroid is underactive, so the pituitary pushes harder. Symptoms include fatigue, weight gain, cold intolerance, dry skin, hair loss, and constipation. Hashimoto's thyroiditis is the most common cause in India.
Frequently Asked Questions
What is a normal TSH level?
Most labs use 0.4–4.0 mIU/L as the reference range. TSH of 4.0–10.0 is considered subclinical hypothyroidism — your thyroid is struggling but still producing enough hormone. Above 10.0 usually requires treatment with levothyroxine.
Why does TSH go UP when the thyroid is LOW?
It seems backwards but makes sense: TSH is a command from the brain to the thyroid. When thyroid hormones are low, the brain sends more TSH ('work harder!'). When thyroid hormones are high, the brain sends less TSH ('slow down!'). High TSH = underactive thyroid.
How often should TSH be checked?
If you are on thyroid medication, check every 6–8 weeks until stable, then every 6–12 months. For screening, adults over 35 should be tested every 5 years. Women planning pregnancy should check TSH, as hypothyroidism affects fetal development.
This information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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