TSH Normal Range, T3 and T4

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TSH, or thyroid-stimulating hormone, is a pituitary hormone that tells the thyroid gland how much thyroid hormone to make, and it is usually the first blood test used to check whether the thyroid is working normally. Free T4 and Free T3 measure the thyroid hormones themselves, in the unbound form that is available to tissues. Published reference intervals for all three are banded by age, shift during pregnancy, and differ from one laboratory to another. That last point is the important one: the range printed on your own report is the one that governs.

What TSH, Free T4 and Free T3 each measure

TSH (thyroid-stimulating hormone, also called thyrotropin) is not a thyroid hormone at all. It is made by the pituitary gland to instruct the thyroid. Because the pituitary responds sensitively to how much thyroid hormone is circulating, TSH often moves before the thyroid hormones do, which is why it is usually measured first.

Free T4 (free thyroxine) is the unbound fraction of thyroxine, the main hormone the thyroid releases. Most T4 in blood travels attached to carrier proteins and is not immediately available to tissues. The free fraction is the part that is.

Free T3 (free triiodothyronine) is the unbound fraction of the more active hormone, most of which is produced by converting T4 in the tissues. Total T3 measures the bound and unbound forms together, which is why its numbers look very different from Free T3.

TSH is reported in mU/L, which is the same unit as mIU/L and as microunits per millilitre. Free T4 is usually reported in ng/dL or pmol/L, and T3 in ng/dL, pg/dL or the equivalent molar units.

TSH reference intervals by age

ARUP Laboratories, an academic reference laboratory affiliated to the University of Utah, publishes age-banded TSH reference intervals in mU/L for people who are not pregnant:

• 0 to 3 days: 5.17 to 14.60
• 4 to 30 days: 0.43 to 16.10
• 1 to 24 months: 0.62 to 8.05
• 2 to 6 years: 0.54 to 4.53
• 7 to 11 years: 0.66 to 4.14
• 12 to 19 years: 0.53 to 3.59
• 20 years and older: 0.27 to 4.20

The pattern is worth noticing. The interval is very wide in the first month of life and narrows steadily through childhood. A newborn TSH that would sit far above the adult interval can be entirely expected at three days old, which is why paediatric samples must be read against a paediatric band.

Other authorities publish adult figures that are close but not identical. MedlinePlus gives an adult range of 0.4 to 4.8 microunits per millilitre, and adds that in older people some laboratories use an upper normal limit even as high as 7 microunits per millilitre. Endotext, hosted by the NIH National Library of Medicine, describes a typical adult interval of about 0.4 to 4.0 mU/l, with mean and median values around 1.0 to 1.5 mU/l.

Free T4 reference intervals by age

ARUP Laboratories publishes Free T4 reference intervals in ng/dL:

• 0 to 3 days: 0.7 to 2.7
• 4 to 30 days: 0.8 to 3.1
• 1 to 23 months: 0.5 to 2.3
• 2 to 6 years: 0.9 to 1.8
• 7 to 11 years: 0.9 to 1.7
• 12 to 19 years: 0.9 to 1.6
• 20 years and older: 0.9 to 1.7
• Pregnancy, first trimester: 0.9 to 1.4
• Pregnancy, second trimester: 0.7 to 1.3

MedlinePlus gives a typical Free T4 range of 0.8 to 1.9 ng/dL, or 10.3 to 24.5 pmol/L, and notes that normal value ranges may vary slightly among different laboratories. It also lists pregnancy, estrogen level, liver problems, severe body-wide illnesses, and inherited changes in a protein that binds T4 among the things that can affect a Free T4 result.

T3: total and free

MedlinePlus publishes these T3 reference ranges:

• Total T3: 78 to 158 ng/dL, or 1.2 to 2.4 nmol/L
• Free T3: 210 to 440 pg/dL, or 3.2 to 6.8 pmol/L

MedlinePlus adds that normal values are age specific for people less than age 20, and that a high T3 level may occur in pregnancy, especially with morning sickness at the end of the first trimester. As with every test on this page, normal value ranges may vary slightly among different laboratories.

T3 is not always requested. Which thyroid tests are ordered depends on the clinical question being asked, so a report may carry TSH alone, or TSH with Free T4, and no T3 at all. If a T3 is not on your report, that is a fair thing to ask about at the appointment.

Pregnancy changes how TSH is read, trimester by trimester

Pregnancy alters thyroid physiology, which is why trimester-specific intervals are published rather than the ordinary adult one. ARUP Consult lists these TSH intervals in mIU/L:

• First trimester: 0.1 to 4
• Second trimester: 0.2 to 4
• Third trimester: 0.3 to 4

ARUP Consult is explicit that these are fallback values, to be used only if more suitable reference intervals are not available. The preferred approach in every trimester is to use assay-specific, population-specific and trimester-specific intervals supplied by the testing laboratory. Free T4 shifts as well: ARUP gives 0.9 to 1.4 ng/dL in the first trimester and 0.7 to 1.3 ng/dL in the second.

Thyroid results in pregnancy are followed closely by the obstetric team as part of routine antenatal care. If you are pregnant or planning a pregnancy, say so when the sample is taken, so that the report is issued against the right interval and read in the right context.

Why two laboratories print two different ranges

Thyroid tests are immunoassays. Different manufacturers use different antibodies, calibrators and analysers, and each laboratory validates its own reference intervals against its own method and the population it serves. That is why the ARUP, MedlinePlus and Endotext adult figures quoted above sit close together without matching exactly, and why none of them is the wrong answer.

Reference ranges vary by laboratory, method, age, sex, pregnancy and clinical context. Read the range printed beside your own result before comparing it with anything found online. A value just outside a printed interval is not a diagnosis, and a value inside one does not rule a problem out. The treating doctor interprets the numbers together with your symptoms, examination, the medicines you take and your previous reports. This page cannot, and does not try to.

How the three results are read together

TSH, Free T4 and Free T3 are interpreted as a set rather than one at a time, because the pituitary and the thyroid respond to each other. A doctor will typically look at whether TSH and the thyroid hormones are moving in the same direction or opposite directions, whether the pattern fits the symptoms, and whether it persists when the test is repeated weeks later.

Several things can move thyroid numbers temporarily, including pregnancy and severe body-wide illness. Some medicines and supplements affect these assays too, so tell the laboratory and your doctor everything you take, including over-the-counter products. Ask whether your sample should be given at a particular time or in a particular way, since instructions differ between laboratories.

Hemoglobin is another common report where the printed range does the work. Our guide to hemoglobin normal ranges explains the same idea for a complete blood count.

When to seek urgent medical care

Outside an emergency, an unexpected thyroid result is a reason to book an appointment with the full report in hand. It is not a reason to change anything on your own.

Frequently asked questions

Sources

ARUP Laboratories Test Directory — Thyroid-Stimulating Hormone (TSH), age-banded reference intervals · ARUP Laboratories Test Directory — Free Thyroxine (Free T4), age-banded and pregnancy reference intervals · MedlinePlus Medical Encyclopedia, US National Library of Medicine (NIH) — TSH test · MedlinePlus Medical Encyclopedia, US National Library of Medicine (NIH) — T4 test · MedlinePlus Medical Encyclopedia, US National Library of Medicine (NIH) — T3 test · Endotext, NCBI Bookshelf (NIH National Library of Medicine) — Clinical Strategies in the Testing of Thyroid Function · ARUP Consult — Thyroid Disease in Pregnancy

Last checked 2 September 2026. How we write and check these pages: editorial policy.