The short answer
TSH is the signal your pituitary gland sends to tell your thyroid how hard to work. It runs backwards: a high TSH usually means an underactive thyroid, and a low one an overactive thyroid. Labcorp’s adult range is 0.45 to 4.5 mIU/L.1,4
- A good result
- 0.45 to 4.5 mIU/L at Labcorp.1 TSH drifts up with age, and in early pregnancy the upper limit is about 4.0.3,7
- If yours is high
- Usually a mildly underactive thyroid. Repeat it before deciding anything, because mild rises can settle on their own. At 10 or more, levothyroxine is usually considered.2,5
Check your result
Type the number from your report. It stays on this page.
- Very low Under 0.10
- Low 0.10 to 0.44
- In range 0.45 to 4.50
- Mildly high 4.51 to 9.99
- High 10.00 or more
- Very low Under 0.10
- Low 0.10 to 0.44
- In range 0.45 to 4.50
- Often watched at your age 4.51 to 9.99
- High 10.00 or more
Your target: 0.1 to 4.0 mIU/L in the first and second trimesters
- Low Under 0.10
- In range 0.10 to 4.00
- Mildly high 4.01 to 10.00
- High 10.01 or more
Your target: 0.45 to 4.50 mIU/L
- Below target Under 0.45
- On target 0.45 to 4.50
- Above target 4.51 or more
Enter your result to see what it means and what to do next.
Got a result from another lab? Ask Picardo about it. The app explains your results, and a physician can follow up.
The 0.45 and 4.5 lines are Labcorp’s adult range.1 The 0.1 and 10 lines come from US and European guidelines,2,4,5 and the pregnancy range from the 2026 ATA guideline, for the first and second trimesters.7 The bar isn’t to scale.
Very low: your thyroid may be overactive
A TSH this low usually means too much thyroid hormone, from an overactive thyroid or too high a dose of thyroid hormone.4 Free T4 and T3 show how much. If either is high, it’s overt hyperthyroidism; if both are normal, it’s subclinical.4 Graves’ disease is the most common cause of an overactive thyroid, and thyroid nodules are a common cause in older people.4
See a clinician in the next week or so, and sooner if your heart is racing or irregular.
- 1 Check free T4 and T3 if they weren’t done.4
- 2 If it stays under 0.1 and you’re 65 or older, have heart disease or its risk factors, thin bones or symptoms, or are past menopause and not on estrogen or a bone medicine, treatment is recommended.4
- 3 If you take biotin, stop it for at least 72 hours, as Labcorp asks, then repeat the test. Biotin can make TSH read falsely low.1,4
Low: recheck before deciding anything
A mildly low TSH can mean a slightly overactive thyroid. It also comes with a serious illness, steroid medicines and early pregnancy.2,4 Guidelines judge it on a TSH that stays low over 3 to 6 months, not on one result.4
Not urgent.
- 1 Check free T4 and T3 to see whether your thyroid hormones are high.4
- 2 Repeat TSH and free T4 within 2 to 6 weeks if you’re 65 or older or have heart disease or thin bones, and within 3 to 6 months otherwise.4
- 3 If it stays low, treatment is considered at 65 or older, or with heart disease, thin bones or symptoms. Younger people without these are usually just watched.4
In range
Your thyroid is working normally. TSH reacts to small changes in thyroid hormone, so it’s the most sensitive single blood test of thyroid function, and a normal result makes a thyroid problem unlikely.2,4
Nothing to worry about.
- 1 If you’re tired, low iron, low B12 and low vitamin D are common next checks.
Mildly high: repeat it before deciding anything
If your free T4 is normal, this is called subclinical hypothyroidism, a mildly underactive thyroid.5 A single high result can settle by itself, and recovering from an illness can raise TSH for a while, so guidelines advise repeating it after 2 to 3 months.2,5
Not urgent.
- 1 Repeat TSH and free T4 in 2 to 3 months, and add TPO antibodies.5
- 2 If it stays high and you have symptoms, ask about a 3-month trial of levothyroxine. If you feel no better, guidelines suggest stopping it.5
- 3 With no symptoms, recheck every 6 months at first.5
- 4 If you’re trying to get pregnant, tell your clinician, because the advice is different.7
High: an underactive thyroid
A TSH of 10 or more usually means your thyroid is underactive, and overtly so if free T4 is low too.2 The most common cause is Hashimoto’s, an autoimmune condition.2 Once a repeat test confirms it, guidelines recommend or suggest levothyroxine for most people up to 70.2,5 Over 70, with a normal free T4, it’s usually kept for people with clear symptoms or high heart risk.5
Very treatable. See a clinician in the next few weeks, or within a week or two if your free T4 is low.
- 1 Check free T4 and TPO antibodies if they weren’t done.2
- 2 Ask about levothyroxine.2,5
- 3 Once you start, TSH is rechecked 4 to 6 weeks after each dose change.3
Above the lab range, but often watched rather than treated at your age
TSH rises with age, and in healthy people over 80 the upper limit is about 7.5 rather than 4.5.3 With a normal free T4, European guidelines advise watching rather than treating below 10 at this age.5 In a large trial of adults 65 and older, levothyroxine didn’t ease symptoms or tiredness at these levels.6
Not a worry on its own, as long as your free T4 is normal.
- 1 If free T4 hasn’t been checked, check it. If it’s low, this is an underactive thyroid that’s usually treated.2
- 2 Otherwise, repeat TSH and free T4 in about 6 months.5
- 3 Treatment is usually considered only if it reaches 10 or more, with clear symptoms or high heart risk.5
Low, which is common early in pregnancy
Early in pregnancy, hCG, the pregnancy hormone, stimulates the thyroid and often pushes TSH this low.7 With a normal free T4 and T3, it doesn’t need treatment, just repeat tests every 2 to 4 weeks. If either is high, a clinician will want to tell this apart from Graves’ disease.7
Usually nothing to worry about, but check free T4 and T3.
- 1 Check free T4 and T3.7
- 2 If both are normal, repeat TSH and free T4 every 2 to 4 weeks.7
- 3 If you take levothyroxine, your dose may be too high. Tell your clinician.7
- 4 Tell your obstetric clinician about a racing heart or severe nausea and vomiting.4
In the pregnancy range
Your TSH is within the range the American Thyroid Association uses in the first and second trimesters when a lab has no range of its own for pregnancy.7
Nothing to worry about, unless you take levothyroxine and it’s 2.5 or more.
Mildly high for pregnancy: check free T4
If your free T4 is low, this is an underactive thyroid. At a TSH of 6 or more it should be treated, and under 6 a repeat test within 3 weeks can confirm it first.7 If free T4 is normal, it’s subclinical hypothyroidism, which often settles, especially under 6.7 Levothyroxine may be considered if it’s found in the first trimester, but isn’t advised after that, because trials found no benefit.7
See your obstetric clinician within 1 to 2 weeks.
- 1 Check free T4 if it wasn’t done, and repeat TSH with it.7
- 2 In the first trimester, ask whether levothyroxine makes sense for you.7
- 3 If you already take levothyroxine, your dose probably needs raising. Contact your clinician now.7
- 4 In the third trimester, the usual adult range applies, so a TSH up to 4.5 can be normal.7
High for pregnancy: it should be treated
In pregnancy, a TSH over 10 should be treated with levothyroxine. If you already take it, your dose needs raising.7
Contact your obstetric clinician this week.
Below target: your dose may be too high
A low TSH on levothyroxine usually means a little more hormone than you need. Over time, too much raises the risk of an irregular heartbeat and bone loss, especially with a TSH under 0.1, in older people and after menopause.3
Not urgent, unless you have palpitations.
On target
Your dose is right. On levothyroxine, US guidelines aim for a TSH within the lab’s normal range.2,3
Nothing to worry about.
Above target: your dose may be too low
A high TSH on levothyroxine means you’re not getting enough. The dose may need raising, or something may be blocking absorption, such as taking it with food or with calcium or iron.3 Over 70, a TSH up to about 6 can be fine.3
Not urgent.
What is a normal TSH level?
Labcorp’s range for adults is 0.45 to 4.5 mIU/L.1 It’s one range for every adult, but TSH drifts up as you get older, and pregnancy lowers it.3,7 Pick the group that fits you in the checker to see your own cutoffs:
Very low: your thyroid may be overactive
A TSH this low usually means too much thyroid hormone, from an overactive thyroid or too high a dose of thyroid hormone.4 Free T4 and T3 show how much. If either is high, it’s overt hyperthyroidism; if both are normal, it’s subclinical.4 Graves’ disease is the most common cause of an overactive thyroid, and thyroid nodules are a common cause in older people.4
See a clinician in the next week or so, and sooner if your heart is racing or irregular.
- 1 Check free T4 and T3 if they weren’t done.4
- 2 If it stays under 0.1 and you’re 65 or older, have heart disease or its risk factors, thin bones or symptoms, or are past menopause and not on estrogen or a bone medicine, treatment is recommended.4
- 3 If you take biotin, stop it for at least 72 hours, as Labcorp asks, then repeat the test. Biotin can make TSH read falsely low.1,4
Low: recheck before deciding anything
A mildly low TSH can mean a slightly overactive thyroid. It also comes with a serious illness, steroid medicines and early pregnancy.2,4 Guidelines judge it on a TSH that stays low over 3 to 6 months, not on one result.4
Not urgent.
- 1 Check free T4 and T3 to see whether your thyroid hormones are high.4
- 2 Repeat TSH and free T4 within 2 to 6 weeks if you’re 65 or older or have heart disease or thin bones, and within 3 to 6 months otherwise.4
- 3 If it stays low, treatment is considered at 65 or older, or with heart disease, thin bones or symptoms. Younger people without these are usually just watched.4
In range
Your thyroid is working normally. TSH reacts to small changes in thyroid hormone, so it’s the most sensitive single blood test of thyroid function, and a normal result makes a thyroid problem unlikely.2,4
Nothing to worry about.
- 1 If you’re tired, low iron, low B12 and low vitamin D are common next checks.
Mildly high: repeat it before deciding anything
If your free T4 is normal, this is called subclinical hypothyroidism, a mildly underactive thyroid.5 A single high result can settle by itself, and recovering from an illness can raise TSH for a while, so guidelines advise repeating it after 2 to 3 months.2,5
Not urgent.
- 1 Repeat TSH and free T4 in 2 to 3 months, and add TPO antibodies.5
- 2 If it stays high and you have symptoms, ask about a 3-month trial of levothyroxine. If you feel no better, guidelines suggest stopping it.5
- 3 With no symptoms, recheck every 6 months at first.5
- 4 If you’re trying to get pregnant, tell your clinician, because the advice is different.7
High: an underactive thyroid
A TSH of 10 or more usually means your thyroid is underactive, and overtly so if free T4 is low too.2 The most common cause is Hashimoto’s, an autoimmune condition.2 Once a repeat test confirms it, guidelines recommend or suggest levothyroxine for most people up to 70.2,5 Over 70, with a normal free T4, it’s usually kept for people with clear symptoms or high heart risk.5
Very treatable. See a clinician in the next few weeks, or within a week or two if your free T4 is low.
What is TSH?
Think of TSH as your body calling for heat. When your thyroid makes too little hormone, the call gets louder and TSH rises. When there’s too much, it goes quiet and TSH falls. That’s why a high TSH means an underactive thyroid.
TSH, short for thyroid-stimulating hormone, comes from the pituitary gland at the base of your brain. It tells your thyroid how much T4 and T3 to make. Small changes in thyroid hormone cause large changes in TSH, which is why it’s the best single first test.4
What causes a high or low TSH?
A high TSH usually means an underactive thyroid. Common causes are:2,3
- Hashimoto’s, an autoimmune condition and the most common cause in the US
- Thyroid surgery or radioactive iodine treatment
- Medicines such as lithium and amiodarone
- Recovering from a serious illness, which can raise TSH for a while
- Too low a dose of levothyroxine, or taking it with food, calcium or iron
A low TSH usually means too much thyroid hormone. Common causes are:4
- Graves’ disease, the most common cause of an overactive thyroid
- Thyroid nodules that make hormone on their own
- Inflammation of the thyroid, which is often temporary
- Too high a dose of thyroid hormone
- Early pregnancy, steroid medicines and a serious illness2
- Biotin supplements, which make TSH read falsely low
Does TSH go up with age?
Yes. In US national data, the upper limit of a normal TSH rises by about 0.3 mIU/L every 10 years after your 30s.2 In healthy people over 80, it’s about 7.5.3 Labcorp still uses one range for every adult.1
A 2025 analysis of US national data found that ranges adjusted for age, sex and race would reclassify about half of people with subclinical hypothyroidism as normal.9 The trial evidence points the same way. In TRUST, 737 adults aged 65 or older with a TSH of 4.6 to 19.9 took levothyroxine or a placebo. After a year, the tablets had made no difference to symptoms or tiredness.6
How is a high or low TSH treated?
It depends on the cause and on how far out of range your TSH is. A mildly high TSH often needs no treatment at all.5
- Levothyroxine, for a high TSH
A daily tablet that replaces the hormone your thyroid isn’t making. TSH is rechecked 4 to 6 weeks after each dose change until it’s in range.3
- How much it helps
- A lot
- How sure we are
- Very sure
- Taking it the same way every day
Food cuts absorption, so take levothyroxine 60 minutes before breakfast or at bedtime, and keep it apart from calcium and iron supplements.3
- How much it helps
- Some
- How sure we are
- Fairly sure
- A lower dose, if your TSH is low on levothyroxine
Brings TSH back into range and avoids the heart rhythm and bone risks of too much thyroid hormone.3
- How much it helps
- A lot
- How sure we are
- Very sure
- Treating an overactive thyroid
Antithyroid medicine, radioactive iodine or surgery, depending on the cause.4
- How much it helps
- A lot
- How sure we are
- Very sure
- Selenium or iodine supplements
Selenium doesn’t prevent or treat an underactive thyroid, and iodine supplements don’t treat one in the US.2 Pregnancy is the exception for iodine, where a supplement is recommended.7
- How much it helps
- A little
- How sure we are
- Fairly sure
Who should get a TSH test?
It’s worth checking if any of these apply to you:
- You have symptoms of an underactive thyroid, such as tiredness, feeling cold, dry skin, constipation or muscle cramps,2 or of an overactive one, such as weight loss, a racing heart, tremor or anxiety.4
- You have type 1 diabetes, pernicious anemia or another autoimmune condition, or a parent, sibling or child with autoimmune thyroid disease, such as Hashimoto’s.2
- You take lithium or amiodarone, or have had radiation to your neck.2
- You’re pregnant or planning a pregnancy and have a risk factor, such as thyroid antibodies, past thyroid disease or an autoimmune condition.7
- You’re over 60. US endocrinologists suggest considering a check at this age.2
For adults with none of these and no symptoms, the US Preventive Services Task Force found too little evidence to recommend for or against testing.8
How to get a TSH test, and what it costs
A TSH test costs $5.00 through Picardo. The Thyroid & Autoimmunity panel adds 12 more tests from the same visit for $76.50.
Thyroid & Autoimmunity panel
TSH is the right first test. The panel adds free T4 and T3 to show how much hormone you’re making, plus inflammation tests, a blood count and kidney and liver tests. It also has ANA and rheumatoid factor, which mean most if you have swollen joints, rashes or other signs of autoimmune disease. See what’s in it
TSH on its own
Only the number this page is about.
- Results in 2 to 3 days, in the app
- Physician follow-up if you want one
- Free Labcorp draw, or $75 at home
- No other fees. HSA and FSA eligible.
It’s also part of the Base Core Annual – Men, Base Core Annual – Women, Heart Health, Brain Health Screening, Pregnancy, Fertility and Postpartum panels, if you want a wider checkup.
Already have a result? Ask Picardo about itQuestions people ask
What time of day should I get a TSH test?
TSH is highest around bedtime and lowest in the late afternoon, and can swing by up to about half over a day.2 So a change of that size within the normal range doesn’t always mean your thyroid has changed. If you’re comparing results, test at a similar time of day.
Does biotin affect a TSH test?
Yes. High doses, common in hair, skin and nail supplements, can make TSH read falsely low and free T4 falsely high, a pattern that looks like an overactive thyroid.4 Labcorp asks you to stop biotin at least 72 hours before the draw.1
Should I take levothyroxine before a TSH test?
For TSH alone, it matters little. TSH reflects your dose over weeks, which is why it’s rechecked 4 to 6 weeks after a change.3 But free T4 rises for several hours after a dose, so if it’s in the same draw, take your levothyroxine afterwards.2
Can being ill change my TSH?
Yes. A serious illness can push TSH down, and it can rise above normal, usually staying under 20, while you recover.2 So unless your thyroid is the suspected cause, it’s best to test once you’re well.
Can I have a thyroid problem with a normal TSH?
Rarely. If the pituitary gland itself isn’t working, TSH can be low, normal or only slightly high while free T4 is low. That’s why free T4 is checked when a pituitary problem is suspected.2
Often checked alongside
Test details
- Labcorp test
- Thyroid-stimulating Hormone (TSH), 004259
- LOINC
- 11580-8
- Sample
- Blood
- Fasting
- Not needed
- Typical lab range
- 0.450 to 4.500 µIU/mL for anyone over 10, with no separate range for older adults1
- Units
- µIU/mL at Labcorp, the same as mIU/L
Sources
- 1 Labcorp. Thyroid-stimulating hormone (TSH), test 004259. Labcorp test menu. Accessed October 28, 2026. www.labcorp.com/tests/004259/thyroid-stimulating-hormone-tsh
- 2 Garber JR, Cobin RH, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Thyroid. 2012;22(12):1200–1235. doi.org/10.1089/thy.2012.0205
- 3 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. doi.org/10.1089/thy.2014.0028
- 4 Ross DS, Burch HB, Cooper DS, et al. 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid. 2016;26(10):1343–1421. doi.org/10.1089/thy.2016.0229
- 5 Pearce SHS, Brabant G, Duntas LH, et al. 2013 ETA guideline: management of subclinical hypothyroidism. Eur Thyroid J. 2013;2(4):215–228. doi.org/10.1159/000356507
- 6 Stott DJ, Rodondi N, Kearney PM, et al. Thyroid hormone therapy for older adults with subclinical hypothyroidism. N Engl J Med. 2017;376(26):2534–2544. doi.org/10.1056/NEJMoa1603825
- 7 Korevaar TIM, Leung AM, Alexander EK, et al. American Thyroid Association 2026 guidelines for thyroid disease in preconception, pregnancy, and postpartum. Thyroid. 2026;36(5):481–544. doi.org/10.1177/10507256261445624
- 8 LeFevre ML; U.S. Preventive Services Task Force. Screening for thyroid dysfunction: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2015;162(9):641–650. doi.org/10.7326/M15-0483
- 9 Li Q, Tang Y, Yu X, et al. Thyroid function reference intervals by age, sex, and race: a cross-sectional study. Ann Intern Med. 2025;178(7):921–929. doi.org/10.7326/ANNALS-24-01559
Updated 3 Nov 2026.
This is general health information, not medical advice: talk to your clinician about your results and before changing any treatment.