# TSH: The first check on your thyroid

> TSH is the first test for an underactive or overactive thyroid. Check your result for your age or pregnancy, and see what a high or low TSH means.

- Also called Thyroid-stimulating hormone and Thyrotropin
- Often on a standard checkup
- No fasting needed
- Web page: https://picardo.health/guides/biomarkers/tsh

## 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]
- **If yours is low:** It can mean an overactive thyroid, or too high a dose of thyroid hormone. Under 0.1 needs a clinician’s attention, especially if you’re 65 or older.[3][4]
- **Should you test?** Yes, if you have symptoms, an autoimmune condition such as type 1 diabetes, or a pregnancy with risk factors. For adults with no symptoms, US experts found too little evidence to advise for or against it.[2][7][8]

## 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:

Which fits you best?

### 70 or younger, not pregnant

| Result (mIU/L) | What it means |
| --- | --- |
| Under 0.10 | Very low: your thyroid may be overactive |
| 0.10 to 0.44 | Low: recheck before deciding anything |
| 0.45 to 4.50 | In range |
| 4.51 to 9.99 | Mildly high: repeat it before deciding anything |
| 10.00 or more | High: an underactive thyroid |

### Over 70

| Result (mIU/L) | What it means |
| --- | --- |
| Under 0.10 | Very low: your thyroid may be overactive |
| 0.10 to 0.44 | Low: recheck before deciding anything |
| 0.45 to 4.50 | In range |
| 4.51 to 9.99 | Above the lab range, but often watched rather than treated at your age |
| 10.00 or more | High: an underactive thyroid |

### Pregnant (target: 0.1 to 4.0 mIU/L in the first and second trimesters)

| Result (mIU/L) | What it means |
| --- | --- |
| Under 0.10 | Low, which is common early in pregnancy |
| 0.10 to 4.00 | In the pregnancy range |
| 4.01 to 10.00 | Mildly high for pregnancy: check free T4 |
| 10.01 or more | High for pregnancy: it should be treated |

### Taking thyroid hormone, such as levothyroxine (target: 0.45 to 4.50 mIU/L)

| Result (mIU/L) | What it means |
| --- | --- |
| Under 0.45 | Below target: your dose may be too high |
| 0.45 to 4.50 | On target |
| 4.51 or more | Above target: your dose may be too low |

If you’re pregnant and take thyroid hormone, pick “Pregnant”. If you’re planning a pregnancy, the usual adult range applies, though on levothyroxine the target is 0.5 to 2.5.[7] After thyroid cancer or with a pituitary condition, your specialist sets a different target.

### Very low: your thyroid may be overactive

**Range:** Under 0.1 mIU/L.

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]

**How worried to be:** See a clinician in the next week or so, and sooner if your heart is racing or irregular.

**What to do next:**

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]

[Test TSH, free T4 and free T3, $15.00](https://app.picardo.health/labs/order?tests=224576,010389&ref=guide-tsh)

### Low: recheck before deciding anything

**Range:** 0.1 to 0.44 mIU/L.

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]

**How worried to be:** Not urgent.

**What to do next:**

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]

[Test TSH, free T4 and free T3, $15.00](https://app.picardo.health/labs/order?tests=224576,010389&ref=guide-tsh)

### In range

**Range:** 0.45 to 4.50 mIU/L.

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]

**How worried to be:** Nothing to worry about.

**What to do next:**

1. If you’re tired, low iron, low B12 and low vitamin D are common next checks.

### Mildly high: repeat it before deciding anything

**Range:** 4.51 to 9.99 mIU/L.

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]

**How worried to be:** Not urgent.

**What to do next:**

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]

[Test TPO antibodies, TSH and free T4, $16.25](https://app.picardo.health/labs/order?tests=006676,224576&ref=guide-tsh)

### High: an underactive thyroid

**Range:** 10 mIU/L or higher.

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]

**How worried to be:** Very treatable. See a clinician in the next few weeks, or within a week or two if your free T4 is low.

**What to do next:**

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]

[Test TSH, free T4 and TPO antibodies, $16.25](https://app.picardo.health/labs/order?tests=224576,006676&ref=guide-tsh)

### Above the lab range, but often watched rather than treated at your age

**Range:** 4.51 to 9.99 mIU/L, over 70.

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]

**How worried to be:** Not a worry on its own, as long as your free T4 is normal.

**What to do next:**

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]

[Test TSH and free T4, $10.00](https://app.picardo.health/labs/order?tests=224576&ref=guide-tsh)

### Low, which is common early in pregnancy

**Range:** Under 0.1 mIU/L, 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]

**How worried to be:** Usually nothing to worry about, but check free T4 and T3.

**What to do next:**

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]

[Test free T4 and free T3, $10.00](https://app.picardo.health/labs/order?tests=001974,010389&ref=guide-tsh)

### In the pregnancy range

**Range:** 0.1 to 4.0 mIU/L, in pregnancy.

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]

**How worried to be:** Nothing to worry about, unless you take levothyroxine and it’s 2.5 or more.

**What to do next:**

1. If you have TPO antibodies, recheck TSH every 4 to 6 weeks until mid-pregnancy.[7]
2. If you take levothyroxine, a TSH under 2.5 is often targeted, with checks about every 4 weeks in the first half of pregnancy. Ask whether your dose should go up.[7]

### Mildly high for pregnancy: check free T4

**Range:** 4.01 to 10 mIU/L, in pregnancy.

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]

**How worried to be:** See your obstetric clinician within 1 to 2 weeks.

**What to do next:**

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]

[Test TSH and free T4, $10.00](https://app.picardo.health/labs/order?tests=224576&ref=guide-tsh)

### High for pregnancy: it should be treated

**Range:** Over 10 mIU/L, in pregnancy.

In pregnancy, a TSH over 10 should be treated with levothyroxine. If you already take it, your dose needs raising.[7]

**How worried to be:** Contact your obstetric clinician this week.

**What to do next:**

1. Ask about starting levothyroxine.[7]
2. Expect TSH checks about every 4 weeks until mid-pregnancy, and once around 30 weeks.[7]

### Below target: your dose may be too high

**Range:** Under 0.45 mIU/L, on thyroid hormone.

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]

**How worried to be:** Not urgent, unless you have palpitations.

**What to do next:**

1. Ask whether your dose should come down.[3]
2. Recheck TSH 4 to 6 weeks after any change.[3]

### On target

**Range:** 0.45 to 4.50 mIU/L, on thyroid hormone.

Your dose is right. On levothyroxine, US guidelines aim for a TSH within the lab’s normal range.[2][3]

**How worried to be:** Nothing to worry about.

**What to do next:**

1. Once your dose is settled, recheck TSH about once a year, and sooner if your weight or medicines change.[3]
2. If you’re planning a pregnancy, ask about a target of 0.5 to 2.5, and contact your clinician as soon as you have a positive test. The dose usually goes up by about a quarter.[7]

### Above target: your dose may be too low

**Range:** 4.51 mIU/L or higher, on thyroid hormone.

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]

**How worried to be:** Not urgent.

**What to do next:**

1. Take levothyroxine the same way every day, 60 minutes before breakfast or at bedtime, and apart from calcium and iron.[3]
2. Ask whether your dose should go up, and recheck 4 to 6 weeks after any change.[3]

## 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 illness[2]
- 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.

- **Recommended:** [the Thyroid & Autoimmunity panel, $76.50](https://app.picardo.health/labs/order?panels=thyroid-autoimmunity&ref=guide-tsh). 13 tests, fast for 12 hours first. 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. [What’s in it](https://picardo.health/guides/panels/thyroid-autoimmunity.md).
- [TSH on its own, $5.00](https://app.picardo.health/labs/order?tests=004259&ref=guide-tsh). Labcorp 004259, no fasting needed.

Every order comes with:

- 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](https://picardo.health/labs/panels/base-core-men), [Base Core Annual – Women](https://picardo.health/labs/panels/base-core-women), [Heart Health](https://picardo.health/labs/panels/heart-health), [Brain Health Screening](https://picardo.health/labs/panels/brain-health), [Pregnancy](https://picardo.health/labs/panels/pregnancy), [Fertility](https://picardo.health/labs/panels/fertility) and [Postpartum](https://picardo.health/labs/panels/postpartum) panels, if you want a wider checkup.

Already have a result? [Ask Picardo about it](https://app.picardo.health/auth).

## Questions 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

- [Free T4](https://picardo.health/guides/biomarkers/free-t4.md): Main thyroid hormone, converted into the more active T3
- [Free T3](https://picardo.health/guides/biomarkers/free-t3.md): Active thyroid hormone that regulates metabolism and energy use
- [TPO antibodies](https://picardo.health/guides/biomarkers/tpo-antibodies.md): A marker of autoimmune thyroid disease
- [Ferritin](https://picardo.health/guides/biomarkers/ferritin.md): How much iron you have in store

## 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 adults[1]
- **Units:** µIU/mL at Labcorp, the same as mIU/L
- **In pregnancy:** Labcorp suggests upper limits of 2.5 in the first trimester and 3.0 after.[1] The 2026 ATA guideline uses 0.1 to 4.0 in the first and second trimesters when a lab has no range of its own.[7]

## Sources

1. Labcorp. Thyroid-stimulating hormone (TSH), test 004259. Labcorp test menu. Accessed October 28, 2026. https://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. https://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. https://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. https://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. https://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. https://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. https://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. https://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. https://doi.org/10.7326/ANNALS-24-01559

Updated 2026-11-03. This is general health information, not medical advice: talk to your clinician about your results and before changing any treatment.