---
title: "TSH test: what it measures, normal levels by age and pregnancy, and what high or low means"
type: biomarker
url: "https://www.test-well.com/biomarkers/tsh"
also_known_as:
  - tsh
  - thyroid stimulating hormone
  - thyrotropin
category: Thyroid
units:
  - mIU/L
  - uIU/mL
order_price_usd: 26.99
order_item: TSH (Thyroid Stimulating Hormone)
order_url: "https://www.test-well.com/tests/tsh"
reviewed_at: 2026-09-17
---

# TSH test: what it measures, normal levels by age and pregnancy, and what high or low means

> TSH is measured with a standard blood draw; no fasting is needed. A typical reference range is 0.450 – 4.50 mIU/L (age 18+; more bands below). At TestWell it's $26.99 all-in as TSH (Thyroid Stimulating Hormone), results in 1–3 business days, drawn at Quest or Labcorp. An out-of-range result is a prompt to look closer, not a diagnosis.

A TSH test measures thyroid-stimulating hormone, the pituitary signal that tells the thyroid how hard to work. Because TSH moves in the opposite direction to thyroid hormone — and moves a lot for a small change — it is the most sensitive single test for an underactive or overactive thyroid. Most adults fall between about 0.45 and 4.5 mIU/L; no fasting is needed.

Also known as: tsh, thyroid stimulating hormone, thyrotropin.

## Key facts

| Fact | Value |
| --- | --- |
| Units | mIU/L / uIU/mL |
| Sample | Blood draw |
| Fasting | Not required |
| Results | 1–3 business days |
| Price | $26.99 |
| Labs | Quest or Labcorp · BioReference in NY/NJ |

## What does a TSH test measure?

TSH is made by the pituitary gland at the base of the brain. Its job is to tell the thyroid to release thyroxine (T4) and triiodothyronine (T3), the hormones that set the pace of metabolism in nearly every cell. The system runs on feedback: when thyroid hormone is low, the pituitary raises TSH to push the gland harder; when thyroid hormone is high, TSH falls.

That feedback is what makes TSH so useful. The relationship is logarithmic — a halving of free T4 roughly doubles or triples TSH — so TSH usually drifts out of range before T4 does. It is why TSH is the first-line thyroid test in essentially every guideline and why a normal TSH, in a person with a healthy pituitary, is strong evidence the thyroid is working normally.

The test is reported in milli-international units per liter (mIU/L; some labs write µIU/mL, which is the same number). It is a simple blood draw and is frequently bundled with free T4, and sometimes free T3 and thyroid antibodies, in a thyroid panel.

## Who should get a TSH test?

TSH is tested when symptoms suggest the thyroid is under- or overactive. Underactive (hypothyroid) symptoms include fatigue, feeling cold, weight gain without a change in habits, constipation, dry skin, hair thinning, a slowed heart rate, heavier periods and low mood. Overactive (hyperthyroid) symptoms include unexplained weight loss, heat intolerance, palpitations, tremor, anxiety, insomnia, frequent bowel movements and lighter periods.

It is also checked in people at higher risk even without clear symptoms: anyone with a goiter or thyroid nodules, a family history of thyroid disease, another autoimmune condition such as type 1 diabetes or celiac disease, previous neck radiation or thyroid surgery, Down syndrome or Turner syndrome, and people taking medications known to affect the thyroid — amiodarone, lithium, interferon and cancer immunotherapy in particular.

Women planning a pregnancy, pregnant, or having trouble conceiving are commonly tested because even mild thyroid dysfunction can affect fertility and pregnancy, and pregnancy has its own reference ranges. Anyone taking levothyroxine needs TSH to guide the dose. Guidelines disagree on whether adults who feel well should be screened routinely; the practical answer is that a TSH is inexpensive and a reasonable check when symptoms or risk factors are present.

## How to get a TSH test and prepare for it

No fasting is required for TSH, and you can have it drawn at any time of day. TSH does have a mild daily rhythm — highest late at night and in the early morning, lowest in the afternoon — so if you are tracking a borderline value over time, drawing at a similar hour each time makes the comparison cleaner.

Two preparation details matter more than timing. First, biotin: high-dose biotin supplements (common in hair, skin and nail products) can interfere with the immunoassays many labs use for TSH and free T4, producing falsely low TSH and falsely high T4. Stop biotin for at least two days before the draw, longer for very large doses. Second, if you take levothyroxine, take it after the blood draw on test day or note the timing for whoever reads the result; the timing affects free T4 more than TSH, but consistency helps.

You can order a TSH test online through TestWell, have blood drawn at a nearby Quest or Labcorp patient service center after a physician reviews the order, and receive results in your portal, typically within a few business days. If the result is abnormal, a free T4 — and often TPO antibodies — is the usual next step, and many people order the thyroid panel from the start to avoid a second visit.

## What is the normal range for TSH?

| Population | Reference range |
| --- | --- |
| age 18+ | 0.450 – 4.50 mIU/L |
| age 18+, pregnancy | 0.100 – 4.00 mIU/L |

Reference intervals differ slightly between labs; the range printed on your report is the one to interpret against. Ranges are usually set so 95% of healthy people fall inside them.

## Normal TSH levels by age and in pregnancy

Most US laboratories report an adult reference range of roughly 0.45 to 4.5 mIU/L, and that is the range TestWell's catalog uses. The exact limits vary slightly by lab and method, so your report's printed range takes precedence. There has been a long debate about whether the upper limit should be lower (around 2.5 to 3.0 mIU/L) because some people with values in the upper part of the range have early autoimmune thyroid disease; most guidelines have kept the wider range, because many people with a TSH of 3 to 4.5 never develop hypothyroidism.

Age changes what counts as normal. Population studies show the TSH distribution shifts upward in older adults, and a TSH of 5 to 7 mIU/L in a person over 70 with a normal free T4 is often within that age group's normal spread rather than a sign of disease. This is one of the reasons mild elevations in older adults are usually rechecked rather than treated.

Pregnancy lowers TSH, particularly in the first trimester, because the pregnancy hormone hCG stimulates the thyroid directly. The American Thyroid Association advises trimester- and population-specific ranges where a lab has them, and where it does not, an upper limit of roughly 4.0 mIU/L in the first trimester with a lower limit around 0.1 mIU/L. Women being treated for hypothyroidism are usually checked more frequently during pregnancy.

| Population | Typical TSH | Notes |
| --- | --- | --- |
| Adults 18+ | 0.45–4.5 mIU/L | Standard adult reference range |
| First trimester of pregnancy | about 0.1–4.0 mIU/L | hCG lowers TSH; use the lab's pregnancy range if it has one |
| Adults over 70 | Upper limit drifts toward 6–7 mIU/L | Mild elevation with normal free T4 is often age-related |
| On levothyroxine | Individual target, usually within the normal range | Rechecked 6–8 weeks after a dose change |

_Ranges are method-dependent; always read your result against the range printed on your report._

## How TSH is read together with free T4

TSH tells you the pituitary's opinion; free T4 tells you the actual thyroid hormone level. Read together, they sort most results into a handful of patterns. A high TSH with a low free T4 is overt hypothyroidism. A high TSH with a normal free T4 is subclinical hypothyroidism, which is frequently rechecked in 6 to 12 weeks before any decision, because a meaningful share of mild elevations normalize on their own. A low TSH with a high free T4 or free T3 is overt hyperthyroidism; a low TSH with normal hormone levels is subclinical hyperthyroidism.

The exceptions are the patterns where TSH and T4 move in the same direction. A low or inappropriately normal TSH with a low free T4 points to a pituitary or hypothalamic problem (central hypothyroidism) rather than the thyroid itself. A high TSH with a high free T4 is rare and raises the question of assay interference, a TSH-secreting pituitary tumor or thyroid hormone resistance — all reasons the result is repeated, often by a different method, before anything else happens.

| TSH | Free T4 | Usual interpretation |
| --- | --- | --- |
| High | Low | Overt hypothyroidism |
| High | Normal | Subclinical hypothyroidism — repeat in 6–12 weeks |
| Low | High | Overt hyperthyroidism |
| Low | Normal | Subclinical hyperthyroidism — repeat; check free T3 |
| Low or normal | Low | Possible central (pituitary) hypothyroidism |
| Normal | Normal | Thyroid function normal |


## What can change a TSH result besides thyroid disease

Recovering from a significant illness can push TSH up for several weeks as the body resets, and being acutely ill can push it down. Medications matter: glucocorticoids, dopamine and high-dose aspirin lower TSH; amiodarone and lithium raise it over time; metformin nudges it down slightly in people on levothyroxine. Biotin interference, discussed above, can make TSH read falsely low. Assay interference from certain antibodies is uncommon but real, which is why a result that makes no clinical sense is rerun on a different platform.

Poor levothyroxine absorption is a common, fixable cause of a high TSH in someone already on treatment: taking the tablet with food, coffee, calcium, iron or a proton-pump inhibitor can reduce how much is absorbed. Finally, TSH varies from day to day by about 10–20% in the same person, so small shifts within the range are noise, not a trend.

## What happens after an abnormal TSH

The next step is almost always a free T4 (and free T3 if TSH is low) to place the result in one of the patterns above, plus TPO antibodies when TSH is high, because Hashimoto's thyroiditis is the most common cause of an underactive thyroid and antibodies predict who progresses. A mildly abnormal TSH with normal hormone levels is typically repeated in 6 to 12 weeks rather than acted on immediately.

Clearly abnormal results, symptoms such as a racing heart, chest pain or confusion, a visibly enlarged thyroid, or any abnormal result during pregnancy warrant prompt clinician review rather than a wait-and-repeat approach. The interpretation sections below walk through the common causes, symptoms and follow-up tests for a high and a low TSH.

## What does a high TSH mean?

A high TSH most often means the thyroid is underactive (primary hypothyroidism): the pituitary is pushing harder because thyroid hormone is low. Mild elevations with a normal Free T4 are called subclinical and are frequently rechecked in 6–12 weeks before anything is done. Recovery from illness, some medicines and biotin-free assay timing also matter.

### Common causes of high TSH

1. Primary hypothyroidism, most often autoimmune (Hashimoto's thyroiditis)
2. Subclinical hypothyroidism — TSH mildly high with a normal Free T4
3. Recovery phase after a non-thyroidal illness
4. Under-replacement on levothyroxine, or poor absorption (taken with food, calcium, iron, coffee)
5. Medications such as lithium and amiodarone
6. Rarely, a TSH-producing pituitary tumor or thyroid hormone resistance

### Symptoms that go with high TSH

- Fatigue and sluggishness
- Feeling cold
- Weight gain despite no change in habits
- Dry skin, hair thinning, constipation
- Low mood, slowed thinking

### What clinicians usually check next

- Free T4 (and Free T3) to see whether hormone levels are actually low
- TPO antibodies to look for Hashimoto's
- Repeat TSH in 6–12 weeks — a single mild elevation often normalizes
- Review of medications and supplements (biotin can distort thyroid assays)

Follow-up tests at TestWell: [Thyroid Peroxidase (TPO) Antibodies](https://www.test-well.com/tests/tpo-antibodies) ($25.99), [Free T3 (Triiodothyronine)](https://www.test-well.com/tests/free-t3) ($30.99), [Biotin (Vitamin B7)](https://www.test-well.com/tests/biotin) ($259.99), [Free T4 (Thyroxine)](https://www.test-well.com/tests/free-t4-test) ($23.99), [T3 Uptake](https://www.test-well.com/tests/t3-uptake-test) ($22.99), [T3, Total (Triiodothyronine)](https://www.test-well.com/tests/total-t3-test) ($24.99).

**How high is too high?** Most labs mark TSH above about 4.5 mIU/L as high. Clinicians usually treat above 10 mIU/L; between 4.5 and 10 with a normal Free T4 the decision depends on symptoms, antibodies, pregnancy plans and a repeat result.

**Can TSH be high without a thyroid problem?** Yes — during recovery from illness, with certain medications, in older adults (the normal range drifts up with age), and transiently for no clear reason. That's why a repeat test is standard before a diagnosis.

## What does a low TSH mean?

A low TSH usually means there is too much thyroid hormone — from an overactive thyroid (Graves' disease, thyroid nodules, thyroiditis) or from taking more thyroid medication than needed. Less often it reflects a pituitary problem, pregnancy's first trimester, or high-dose biotin interfering with the test. Free T4 and Free T3 tell the two apart.

### Common causes of low TSH

1. Hyperthyroidism: Graves' disease, toxic nodules, or thyroiditis (an inflamed thyroid leaking hormone)
2. Over-replacement with levothyroxine or other thyroid medication
3. Subclinical hyperthyroidism — TSH low with normal Free T4 and Free T3
4. First-trimester pregnancy (hCG stimulates the thyroid)
5. High-dose biotin supplements distorting the assay
6. Pituitary (central) hypothyroidism — low TSH with a low Free T4
7. Recent glucocorticoid or dopamine use, or acute illness

### Symptoms that go with low TSH

- Racing or irregular heartbeat
- Anxiety, tremor, sweating, heat intolerance
- Weight loss with normal or increased appetite
- Trouble sleeping
- Loose stools
- Sometimes no symptoms at all when mild

### What clinicians usually check next

- Free T4 and Free T3 — high confirms hyperthyroidism; low points to the pituitary
- TSH receptor antibodies (TRAb/TSI) when Graves' is suspected
- Review of thyroid medication dose and biotin use
- Repeat in 6–8 weeks for mild results without symptoms

Follow-up tests at TestWell: [Free T3 (Triiodothyronine)](https://www.test-well.com/tests/free-t3) ($30.99), [Biotin (Vitamin B7)](https://www.test-well.com/tests/biotin) ($259.99), [Free T4 (Thyroxine)](https://www.test-well.com/tests/free-t4-test) ($23.99), [T3 Uptake](https://www.test-well.com/tests/t3-uptake-test) ($22.99), [T3, Total (Triiodothyronine)](https://www.test-well.com/tests/total-t3-test) ($24.99), [TSI (Thyroid-Stimulating Immunoglobulin)](https://www.test-well.com/tests/thyroid-stimulating-immunoglobulin-tsi) ($114.99).

### Seek care promptly if

- A low TSH with a very fast heart rate, fever, confusion or severe agitation can be thyroid storm — emergency care

**Is a low TSH dangerous?** Sustained untreated hyperthyroidism raises the risk of atrial fibrillation and bone loss, so it's evaluated rather than ignored — but a mildly low TSH with normal Free T4 is often monitored, not treated.

**I take levothyroxine and my TSH is low. What does it mean?** Most often that the dose is a little high. Don't change it yourself — the prescriber adjusts and rechecks in 6–8 weeks.

## How often should you retest?

If you take levothyroxine, recheck TSH about 6–8 weeks after any dose change — it takes that long for the level to settle — and then every 6–12 months once stable, per the American Thyroid Association. Without known thyroid disease there's no fixed interval; a repeat is reasonable when symptoms change or a first result was borderline.

## How do you get tested for TSH?

| Order | Type | Price | Includes |
| --- | --- | --- | --- |
| [TSH (Thyroid Stimulating Hormone)](https://www.test-well.com/tests/tsh) | Single test | $26.99 | This marker |
| [General Wellness Panel](https://www.test-well.com/tests/general-wellness-panel) | Panel | $49.99 | 4 tests |
| [Essential Thyroid Panel](https://www.test-well.com/tests/essential-thyroid-panel) | Panel | $49.99 | 3 tests |
| [Post-COVID Recovery Panel](https://www.test-well.com/tests/post-covid-panel) | Panel | $99.99 | 7 tests |
| [Erectile Dysfunction Panel](https://www.test-well.com/tests/erectile-dysfunction-panel) | Panel | $114.99 | 7 tests |

## Quest vs Labcorp vs BioReference

| Lab | Available | Price | Notes |
| --- | --- | --- | --- |
| Quest Diagnostics | Yes | $26.99 | Choose Quest at checkout; walk-in patient service centers in every state TestWell serves outside NY and NJ. |
| Labcorp | Yes | $27.99 | Choose Labcorp at checkout; walk-in patient service centers in every state TestWell serves outside NY and NJ. |
| BioReference (NY & NJ) | Yes | $24.99 | New York and New Jersey orders route here automatically — state rules keep Quest and Labcorp from accepting self-ordered draws. |

## Common questions about TSH

### What is a normal TSH level?

For most adults, about 0.45 to 4.5 mIU/L, with slight variation between labs. The upper limit drifts higher in people over 70, and pregnancy lowers the range, especially in the first trimester. Read your value against the range printed on your own report.

### Is a TSH test enough on its own to check my thyroid?

As a first test, usually yes — in someone with a healthy pituitary a normal TSH makes thyroid disease unlikely. If TSH is abnormal, free T4 (and sometimes free T3 and TPO antibodies) is needed to interpret it, which is why many people order a thyroid panel from the start.

### Do I need to fast for a TSH test?

No. Eating does not meaningfully change TSH. What does matter is stopping high-dose biotin for a couple of days beforehand and, if you take levothyroxine, taking it after the draw or noting when you took it.

### What TSH level means hypothyroidism?

A TSH above the reference range with a low free T4 is overt hypothyroidism. A TSH above the range with a normal free T4 is subclinical hypothyroidism; clinicians generally treat when TSH is above about 10 mIU/L and individualize between 4.5 and 10 based on symptoms, antibodies, pregnancy plans and a repeat result.

### Can stress or illness raise TSH?

Recovery from a significant illness can raise TSH for weeks, and acute illness or high-dose steroids can lower it. Everyday psychological stress has little direct effect on TSH. A result that does not fit your symptoms is worth repeating once you are well.

### Do I need a doctor's order to test my tsh?

No. TestWell's licensed physician network reviews and approves your order — usually within minutes. You can place an order online without an in-person visit or a referral from your own doctor.

### How long does it take to get TSH results?

Most TSH results are available in 1–3 business days after your specimen arrives at the lab. You'll get an email the moment your results are ready, with everything viewable in your TestWell portal.

### How much does a TSH test cost?

Our TSH (Thyroid Stimulating Hormone) starts at $26.99. That's the all-in price — no copays, no insurance hoops, no surprise bills. HSA and FSA cards are accepted.

### Do I need to fast before my TSH test?

Fasting is not required for the TSH test. You can have your blood drawn any time of day.

### Which lab will process my TSH test?

Your test will be processed by Quest Diagnostics, Labcorp, or BioReference depending on which is closest to you and which lab carries the test. All three are CLIA-certified and trusted by hospitals nationwide. You'll choose your lab during checkout from 4,000+ locations.

## Keep reading

- [Blood Tests for Thyroid Symptoms](https://www.test-well.com/guides/blood-tests-for-thyroid-symptoms)
- [Fatigue: which blood tests?](https://www.test-well.com/symptoms/fatigue)
- [Always feeling cold: which blood tests?](https://www.test-well.com/symptoms/cold-intolerance)
- [Unexplained weight gain: which blood tests?](https://www.test-well.com/symptoms/weight-gain)
- [Hair loss: which blood tests?](https://www.test-well.com/symptoms/hair-loss)
- [Heart palpitations: which blood tests?](https://www.test-well.com/symptoms/heart-palpitations)
- [Anxiety: which blood tests?](https://www.test-well.com/symptoms/anxiety)
- [Constipation: which blood tests?](https://www.test-well.com/symptoms/constipation)
- [Brain fog: which blood tests?](https://www.test-well.com/symptoms/brain-fog)
- [Before your test: Biotin supplements](https://www.test-well.com/prep/biotin)
- [Before your test: Thyroid medication timing](https://www.test-well.com/prep/levothyroxine-timing)
- [Before your test: Time of day](https://www.test-well.com/prep/time-of-day)
- [Before your test: Recent illness](https://www.test-well.com/prep/recent-illness)

## Sources

- [American Thyroid Association](https://www.thyroid.org/thyroid-function-tests/)
- [American Thyroid Association — Guidelines for the Treatment of Hypothyroidism (2014)](https://doi.org/10.1089/thy.2014.0028)
- [American Thyroid Association — Guidelines for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum (2017)](https://doi.org/10.1089/thy.2016.0457)
- [Surks & Hollowell — Age-specific distribution of serum TSH in the US population (JCEM 2007)](https://doi.org/10.1210/jc.2007-1499)
- [FDA Safety Communication — Biotin may interfere with lab tests](https://www.fda.gov/medical-devices/safety-communications/update-fda-warns-biotin-may-interfere-lab-tests-fda-safety-communication)

## Related biomarkers

- [Free T4](https://www.test-well.com/biomarkers/free-t4)
- [Free T3](https://www.test-well.com/biomarkers/free-t3)
- [Reverse T3](https://www.test-well.com/biomarkers/reverse-t3)
- [TPO Antibodies](https://www.test-well.com/biomarkers/tpo-antibodies)
- [Thyroglobulin Antibodies](https://www.test-well.com/biomarkers/thyroglobulin-antibodies)

- [Reference range lookup tool](https://www.test-well.com/tools/reference-range-lookup)
- [Lab unit converter](https://www.test-well.com/tools/lab-unit-converter)
- [All biomarkers](https://www.test-well.com/biomarkers)

---

Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-17. Review policy: https://www.test-well.com/reviewers/youmna-distefano-md

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Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.