Also seen on reports as: Thyrotropin, Serum TSH
What is TSH?
TSH (Thyroid Stimulating Hormone) is a hormone made by the pituitary gland, a small gland at the base of the brain. The pituitary releases TSH to tell the thyroid gland (in the front of the neck) how much thyroid hormone to produce.
When thyroid hormone levels in the blood are too low, the pituitary releases more TSH to push the thyroid to make more. When thyroid hormone levels are too high, the pituitary holds back on TSH. So TSH usually moves in the opposite direction to the actual thyroid hormones (T3 and T4).
The test is run on a small blood sample drawn from a vein. Most NABL-accredited Indian labs report TSH in microunits per millilitre (µIU/mL or mIU/L).
Why doctors order it
TSH is the most commonly ordered thyroid test. It is used as the first-line test to check thyroid function — whether the thyroid is producing too little hormone (hypothyroidism) or too much (hyperthyroidism).
Doctors commonly order TSH when symptoms suggest a thyroid problem — unexplained weight gain or loss, persistent tiredness, hair thinning, dry skin, constipation, irregular periods, fertility problems, palpitations, heat or cold intolerance, or mood changes. It is also part of many routine annual health checks in Indian adults.
TSH is a standard part of antenatal screening, pre-conception evaluation, infertility work-up, and follow-up of anyone already on thyroid medication. In someone with known thyroid disease, TSH is checked periodically to see if the dose of medication needs adjustment.
What the result means
TSH alone does not tell the whole thyroid story, but it is a sensitive starting point. A high TSH usually points to an underactive thyroid (the pituitary is shouting at a sluggish gland); a low TSH usually points to an overactive thyroid or to suppression from medication. When TSH is abnormal, doctors typically follow up with free T4 (and sometimes free T3) to confirm what is happening.
Mildly raised TSH with normal T4 is called 'subclinical hypothyroidism'. It is common, particularly in Indian women, and may or may not need treatment depending on the exact value, symptoms, presence of thyroid antibodies, age, and whether the person is pregnant or planning a pregnancy.
Reference ranges vary slightly between Indian labs and between life stages. Pregnancy uses different (tighter) targets — particularly in the first trimester. Newborns are screened separately because their thyroid physiology differs from adults.
Reference range
Values in µIU/mL (or mIU/L) — non-pregnant adults
- Typical adult reference range
- Roughly 0.4 – 4.0 µIU/mL (varies slightly by lab)
- Subclinical hypothyroidism
- TSH above the upper limit with a normal free T4
- Overt hypothyroidism
- TSH high with a low free T4
- Hyperthyroidism
- TSH low (often below 0.1) with high free T4 and/or T3
- Pregnancy targets (trimester-specific)
- Stricter than non-pregnant — typically TSH below ~2.5 in the first trimester
Reference ranges differ between NABL-accredited Indian labs because TSH assays are not fully standardised across manufacturers. Pregnancy, newborns, and patients on certain medications use different cut-offs — your doctor reads the value in context.
In India
What this test means for an Indian reader
Hypothyroidism is common in India — population studies report prevalence in the 8–12% range, higher in women. Universal Salt Iodisation has reduced iodine-deficiency hypothyroidism; autoimmune (Hashimoto's) cases now dominate diagnoses, especially among women aged 30–60.
Reference ranges vary slightly by laboratory and by trimester in pregnancy. Most NABL-accredited Indian labs report a TSH range close to 0.4–4.0 mIU/L for non-pregnant adults; your doctor interprets borderline values in context.
Indian guidelines & references
- Indian Thyroid Society (ITS)
- AIIMS thyroid clinic protocols
- ICMR National Iodine Deficiency Disorders Control Programme
Common factors that affect the result
TSH levels follow a natural daily rhythm — typically higher in the early morning and lower in the late afternoon and evening. Acute illness, hospitalisation, intense stress, and disturbed sleep can shift TSH temporarily, sometimes lowering it (a pattern called 'sick euthyroid' or non-thyroidal illness syndrome).
Several medications affect TSH. Steroids, dopamine, opioids, and amiodarone can suppress TSH. Biotin supplements (often taken for hair/nail health, including in some popular Indian over-the-counter products) can falsely lower or raise TSH on many lab assays — most guidelines advise stopping biotin for 48–72 hours before a thyroid test.
Pregnancy lowers TSH on average — particularly in the first trimester, when HCG (the pregnancy hormone) cross-stimulates the thyroid. After delivery, TSH typically returns to baseline over weeks to months, though some women develop post-partum thyroid changes that need follow-up.
When to talk to your doctor
- Your TSH is above the lab's upper limit for the first time, or has crept up from previous readings.
- Your TSH is below the lab's lower limit, particularly if you have symptoms like palpitations, unexplained weight loss, tremor, or heat intolerance.
- You are on thyroid medication and your TSH has moved further from your doctor-set target — up or down.
- You are planning a pregnancy, are pregnant, or have recently delivered — pregnancy-specific TSH targets apply.
- You take biotin or any hair/skin/nail supplement that contains biotin — your doctor may need to repeat the test off biotin.
Related tests
Sources
- Indian Thyroid Society Guidelines for Management of Hypothyroidism
- ICMR National Iodine Deficiency Disorders Control Programme — Indian Council of Medical Research
- ATA / AACE Clinical Practice Guidelines for Hypothyroidism — American Thyroid Association
- WHO Thyroid Disorders Guidance — World Health Organization
- FOGSI Guidelines on Thyroid in Pregnancy — Federation of Obstetric and Gynaecological Societies of India
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