Thyroid Test

TSH Test (Thyroid Stimulating Hormone)

TSH is the single most important thyroid test. It acts like a thermostat for your thyroid: when thyroid function is off, TSH rises or falls. Here's what your result means.¹

Written by Suman Konda, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last reviewed and updated: 26 September 2026 · How we check our content

What is TSH?

TSH (Thyroid Stimulating Hormone) is produced by the pituitary gland in the brain. It tells the thyroid gland how much thyroid hormone (T3 and T4) to produce. TSH works like a thermostat: if thyroid hormone levels are low, the pituitary pumps out more TSH to stimulate the thyroid. If thyroid hormone is too high, TSH drops to signal the thyroid to slow down. This is why TSH moves in the opposite direction to thyroid hormones. Because this feedback loop is so sensitive, TSH usually changes before thyroid hormone levels themselves move outside their normal range, which is why it is the best first-line screening test for thyroid function.

TSH Normal Range

Group	Normal TSH (mIU/L)
Adults (general)	0.4 – 4.0 mIU/L
Adults (many labs)	0.5 – 5.0 mIU/L
Pregnancy (1st trimester)	0.1 – 2.5 mIU/L
Pregnancy (2nd trimester)	0.2 – 3.0 mIU/L
Pregnancy (3rd trimester)	0.3 – 3.0 mIU/L
Elderly (>70 yrs)	Up to 6.0 may be acceptable

TSH Test (Thyroid Stimulating Hormone): reference intervals by group (mIU/L), drawn from the table above. Intervals differ between laboratories: compare your result against the range printed on your own report.

What does HIGH TSH mean?

HIGH TSH above 4.0 mIU/L: Hypothyroidism

High TSH means your thyroid is underperforming: the pituitary is shouting louder to try to get the sluggish thyroid to produce more hormone. This is hypothyroidism (underactive thyroid). Most common cause: Hashimoto's thyroiditis (autoimmune attack on the thyroid). Symptoms: fatigue, weight gain, feeling cold, constipation, hair loss, dry skin, depression, heavy periods, brain fog. Treatment: levothyroxine tablet once daily, usually lifelong. Most people feel dramatically better within 4–8 weeks of starting treatment.

What does LOW TSH mean?

LOW TSH below 0.4 mIU/L: Hyperthyroidism

Low TSH means your thyroid is overproducing hormones: the pituitary has gone quiet because there's already too much thyroid hormone. This is hyperthyroidism (overactive thyroid). Most common cause: Graves' disease (autoimmune), toxic nodular goitre, or excess thyroid medication. Symptoms: weight loss despite increased appetite, palpitations (fast/irregular heartbeat), anxiety, trembling hands, heat intolerance, sweating, diarrhoea, bulging eyes (Graves'). Requires prompt treatment, untreated hyperthyroidism can cause atrial fibrillation and bone loss.

Scroll sideways to see the whole diagram

How TSH and free T4 combine to give a thyroid diagnosis.

What the grid shows. TSH and free T4 are interpreted together. A high TSH with a low free T4 is overt hypothyroidism; a high TSH with a normal free T4 is subclinical hypothyroidism, which is the commonest abnormal pattern and often needs monitoring rather than treatment. A low TSH with a high free T4 is overt hyperthyroidism, and a low TSH with a normal free T4 is the subclinical form. The one combination that points away from the thyroid itself is a low TSH with a low free T4, which suggests a pituitary cause. The counter-intuitive part is that a high TSH means an underactive gland, because TSH is the signal telling the thyroid to work harder.

Normal TSH levels by age

The upper limit of the TSH reference interval is not fixed across adult life: it rises steadily with age. This matters because a value that would be called abnormal in a 25-year-old can be entirely normal at 75, and applying one adult range to everyone is a recognised cause of overdiagnosis in older people.

In an analysis of NHANES III data stratified by age decade, the 97.5th percentile of TSH rose from 3.56 mIU/L in people aged 20 to 29 to 7.49 mIU/L in those over 80, with most older people whose TSH exceeded the conventional 4.5 mIU/L cut-off still falling within their own age-specific range.³ A Scottish population study of people with no known thyroid disease found the same direction of effect, with the 97.5th centile rising from 3.98 to 5.94 mU/L across the adult age span.

Age group	Approximate upper limit (97.5th percentile)	What it means in practice
20–29 years	~3.6 mIU/L	The conventional 4.0 mIU/L cut-off is, if anything, slightly generous at this age
30–49 years	~4.0–4.5 mIU/L	Close to the standard laboratory upper limit
50–69 years	~4.5–5.5 mIU/L	Mildly raised values are common and often need no treatment
70–79 years	~5.5–6.5 mIU/L	A TSH of 5 or 6 is frequently a normal age-related finding
80+ years	~7.5 mIU/L	Treating to a young adult target may do more harm than good

These figures describe how the population distribution shifts with age; they are not a substitute for the interval your own laboratory prints, which is what your result should be read against. The practical consequence is that in an older person with a mildly raised TSH and a normal free T4, the finding is often watched rather than treated. Applying age-, sex- and race-specific intervals to the NHANES data reclassified 48.5% of people labelled with subclinical hypothyroidism as normal.

Age also affects the lower end differently in pregnancy, where hCG stimulates the thyroid directly and TSH commonly falls below the non-pregnant lower limit in the first trimester. Pregnancy-specific intervals should always be used in that setting.

Subclinical thyroid disease

Subclinical Hypothyroidism: high TSH + normal T4

TSH between 4.0–10 mIU/L with normal free T4 = subclinical hypothyroidism. Many people have no symptoms. Whether to treat depends on TSH level, symptoms, age, and pregnancy status. Pregnant women with subclinical hypothyroidism are always treated: it affects fetal brain development.

Thyroid myths vs facts

Thyroid testing attracts more folklore than almost any other blood test. Here is what the evidence actually says:

MYTH A TSH of 5 means lifelong thyroid tablets.

Fact: A TSH between 4 and 10 with normal free T4 is subclinical hypothyroidism, and guidelines suggest rechecking in 6–12 weeks before any treatment decision. Thyroid levels wobble with illness, sleep and even time of day — one mildly raised reading is not a lifetime prescription.

MYTH A normal TSH rules out every thyroid problem.

Fact: TSH is the best first screen, but it is not infallible. In central hypothyroidism (a pituitary cause), TSH can look misleadingly normal while thyroid hormone is low. Symptoms plus free T4 complete the picture — discuss persistent symptoms with your doctor even if TSH is normal.

MYTH Supplements can’t affect the result.

Fact: High-dose biotin (vitamin B7), common in hair, skin and nail supplements, interferes with the TSH assay and can produce misleading results. Tell the lab about every supplement you take — it is the interference patients forget to mention most often.

MYTH It doesn’t matter what time of day you test.

Fact: TSH follows a daily rhythm, peaking in the early morning and falling through the day. A TSH drawn at 8 am and one at 4 pm aren’t strictly comparable, so test at roughly the same morning time each round when tracking a trend.

MYTH Take your thyroid tablet before the test so the reading reflects treatment.

Fact: Take the day’s levothyroxine after the blood draw, not before. A tablet taken just beforehand can distort the reading and make a well-controlled dose look wrong. Mention your usual timing to the lab.

Your TSH result: what to do next

Got your report and wondering what the number means for you? Follow the branch that matches your situation — every path ends with your doctor, because TSH is never interpreted alone:

Your situation	Sensible next step
TSH 4–10, normal free T4, no symptoms, not pregnant	Usually just rechecked in 6–12 weeks. Discuss symptoms, antibodies and family history with your doctor before considering treatment.
TSH above 10, whatever the T4	Discuss promptly with your doctor — this range usually warrants treatment evaluation.
Any abnormal TSH in pregnancy or while planning pregnancy	Discuss promptly. Thyroid levels affect foetal development, and targets are tighter in pregnancy.
TSH below 0.4 (suppressed)	Discuss promptly with your doctor; do not ignore a suppressed TSH even if you feel well.
On levothyroxine and TSH is out of range	Do not adjust the dose yourself. TSH is rechecked about 6–8 weeks after any dose change — the feedback loop needs that long to settle.
First abnormal result during illness, stress or poor sleep	Ask your doctor about repeating the test once you have recovered; acute illness can temporarily shift thyroid levels.

Bring your medication and supplement list to the discussion — biotin, recent dose changes and the time of day you tested all help your doctor read the result correctly.

TSH test price in India: typical bands across major lab chains

A standalone TSH test is inexpensive; full thyroid profiles (TSH + T3 + T4) cost more. Typical list-price bands for a standalone TSH test:

Lab chain	Typical TSH price band	Notes
Dr Lal PathLabs	Typically &rupee;450–&rupee;650	Wide network; online booking often slightly cheaper
Metropolis Healthcare	Typically &rupee;400–&rupee;550	Frequent online discounts
Thyrocare (via partner labs)	Typically &rupee;300–&rupee;450	Often the lowest list price; home collection available
Apollo 24\|7	Typically &rupee;350–&rupee;500	Integrated with Apollo hospitals
Orange Health	Typically &rupee;450–&rupee;600	Home-collection focused in metro cities

These are approximate bands, not quotes: prices change often and vary by city, and home collection can add a small fee. Bundled thyroid profiles (T3/T4/TSH) typically cost roughly double the standalone test. Where possible, choose a NABL-accredited lab.

Monitoring treatment with TSH

For people taking levothyroxine for an underactive thyroid, TSH is the main measure used to adjust the dose. Because the thyroid system responds slowly, TSH is usually rechecked around 6–8 weeks after any dose change rather than sooner, which is roughly how long it takes the pituitary-thyroid feedback loop to settle at a new steady state, per American Thyroid Association treatment guidance.²

Timing and consistency help: TSH is naturally higher in the early morning, and biotin supplements can interfere with the test, so it is worth mentioning any supplements you take.

Questions to ask your doctor

Should I also check free T3 and free T4?
Should I test thyroid antibodies (anti-TPO) to check for Hashimoto's?
My TSH is 5.5. Do I need medication or just monitoring?
I'm pregnant. What TSH level is safe for my baby?

Frequently Asked Questions

Do I need to fast for a TSH test?

No fasting is required, but as TSH varies through the day, a consistent time (often morning) is preferred when monitoring treatment.

What is a normal TSH level?

Most laboratories use a range of roughly 0.4–4.0 mU/L, though the ideal target is individualised, particularly in pregnancy and older age.

Can supplements affect my TSH result?

Yes. Biotin (vitamin B7), common in hair and nail supplements, can interfere with some thyroid assays and give misleading results, so pause it before testing if advised.

How soon after changing my thyroid dose should TSH be checked?

Usually after about 6–8 weeks, because the thyroid system takes time to reach a new steady state.

My TSH is 5.2 but my T4 is normal. Do I need treatment?

Not necessarily — this is subclinical hypothyroidism, and it is often simply watched and rechecked in two to three months. Treatment depends on symptoms, thyroid antibodies, cholesterol, and pregnancy plans. Discuss the full picture with your doctor rather than the TSH alone.

Should I test TSH at the same time of day each time?

Yes, ideally. TSH is highest in the early morning and lower by afternoon, so a morning draw kept consistent across tests gives the most comparable trend. An afternoon result that looks a touch lower may just be the clock.

Can stress or illness change my TSH?

Acute illness can temporarily suppress TSH even when the thyroid is fine — the so-called non-thyroidal illness effect. That is why doctors usually retest after recovery rather than acting on a TSH drawn during a hospital stay or serious infection.

I took my thyroid tablet before the test. Does it matter?

It can. Levothyroxine taken just before the draw may distort the result and mislead dose decisions. The usual advice is to take the tablet after the blood is drawn — and to tell the lab what you actually did, so the result is read correctly.

How much does the Thyroid test cost in India?

The Thyroid test typically costs ₹350–₹700 in India, though prices vary by city and lab. Choose a NABL-accredited lab where possible — and remember the reference range printed on your own report is the one that counts. Discuss the result with your doctor.

Pharmacist's practical notes

TSH follows a daily rhythm — it peaks in the early morning hours and falls through the day. A TSH drawn at 8 am and one drawn at 4 pm aren't strictly comparable, so test at roughly the same morning time each round if you are tracking a trend.

High-dose biotin — common in hair, skin and nail supplements — can interfere with the TSH assay and produce misleading results. Tell the lab about every supplement you take; it is the interference patients forget to mention most often.

Take the day's levothyroxine after the blood draw, not before. A tablet taken just before the test can distort the reading and make a well-controlled dose look wrong. Mention your usual timing to the lab.

A mildly raised TSH with normal T4 — subclinical hypothyroidism — often just gets watched and repeated in a couple of months rather than treated immediately. Not every raised TSH means lifelong tablets; the decision weighs symptoms, antibodies and circumstances, and it belongs to your doctor.

In India

Indian labs report TSH in mIU/L (the same as µIU/mL), so the ranges on this page apply directly. Typical prices are compared chain-by-chain in the table above; bundled thyroid profiles (T3/T4/TSH) cost more than a standalone TSH.

Where possible, choose a NABL-accredited lab. Reference ranges can differ slightly depending on the analyser a lab uses, so the range printed on your own report is the one that counts — not a number from a website.

References

Sources cited on this page. PubMed links open the original abstract.

Surks MI, Ortiz E, Daniels GH, et al. Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. JAMA. 2004;291(2):228–238. PMID 14722150 · doi:10.1001/jama.291.2.228
Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid. 2014;24(12):1670–1751. PMID 25266247 · doi:10.1089/thy.2014.0028
Surks MI, Hollowell JG. Age-Specific Distribution of Serum Thyrotropin and Antithyroid Antibodies in the US Population: Implications for the Prevalence of Subclinical Hypothyroidism. J Clin Endocrinol Metab. 2007;92(12):4575–4582. PMID 17911171 · doi:10.1210/jc.2007-1499

Medical Disclaimer: This page is for general educational purposes only. It does not constitute medical advice. Always consult a qualified doctor before making any health decisions.