Dr. Prabhat AryaMD · Internal Medicine
ConditionsKnow your condition

Your thyroid report, line by line.

A thyroid report has one main number, TSH, and a few that explain it. A TSH just outside the range is very common, often settles on a repeat test, and is rarely urgent.

Reviewed by Dr. Prabhat Arya, MBBS, MD (Internal Medicine)

Reviewed · Next review · Sources: British Thyroid Foundation, MedlinePlus, NHS

Send your report for ₹199See every value

Read this first.

Go by the range printed on your own report. The ranges below are typical adult ranges; labs use different machines and units, so their ranges differ more for thyroid tests than for most others. Pregnancy has its own ranges.

Read TSH first. It is a message from the brain’s pituitary gland to the thyroid. When the thyroid is slow, the brain shouts louder and TSH goes up. When the thyroid is overactive, TSH goes down. So a high TSH means an underactive thyroid, and a low TSH means an overactive one. Then T4 (or free T4) tells you how much hormone is actually there.

One slightly-off TSH is rarely a reason to start a tablet. TSH can go up for a few weeks after an illness, and many mild changes come back to normal on a repeat test 6–12 weeks later. Biotin supplements (often taken for hair and nails) can upset thyroid results and give a false picture: tell the lab, and ask whether to stop them for a few days before the test.

Compare with your last report. If you already take a thyroid tablet, the report mainly tells whether the dose is right, and it is best checked at least six weeks after any change of dose.

Every value, one by one.

T3 (total)

Triiodothyronine: the active thyroid hormone, including the part bound to proteins in the blood

Typical adult range About 80–200 ng/dL (labs vary; some print 0.8–2.0 ng/mL)

High usually means
Can mean an overactive thyroid, especially if TSH is low. Pregnancy and the contraceptive pill raise the proteins that carry thyroid hormone, so total T3 can read high with a normal TSH, which is not a disease.
Low usually means
Usually during or after any illness, fasting or poor eating, when the body turns down T3 for a while. On its own, with a normal TSH, a low T3 rarely means thyroid disease.
Usually nothing to worry about when
It is slightly off and TSH is normal.
See a doctor when
This week if it is high together with a low TSH and you have a racing heart, weight loss or tremor.

T4 (total)

Thyroxine: the main hormone the thyroid makes, including the part bound to proteins

Typical adult range About 5–12 µg/dL (labs vary)

High usually means
With a low TSH, an overactive thyroid. With a normal TSH, often just pregnancy or the contraceptive pill, which raise the carrier proteins.
Low usually means
With a high TSH, an underactive thyroid. With a normal TSH, often a low level of carrier proteins (for example with liver or kidney disease) rather than a thyroid problem.
Usually nothing to worry about when
It is slightly off and TSH is normal.
See a doctor when
Within a week or two if it is low with a high TSH, or high with a low TSH.

TSH

Thyroid-stimulating hormone: the pituitary’s signal telling the thyroid how hard to work. Sometimes written “TSH, ultrasensitive”

Typical adult range About 0.4–4.0 mIU/L (many Indian labs print a top limit between 4.2 and 5.5)

High usually means
Usually an underactive thyroid (hypothyroidism). In India the commonest cause is Hashimoto’s thyroiditis, where the body’s own defences slowly damage the thyroid; anti-TPO is then positive. A mild rise (up to about 10) with a normal free T4 is called subclinical hypothyroidism: it often needs only a repeat test, not a tablet. TSH can also rise for a few weeks while recovering from an illness, and runs a little higher in older people. If you take a thyroid tablet, a high TSH usually means the dose is too low or the tablet is not being taken regularly or on an empty stomach.
Low usually means
Usually an overactive thyroid, or, if you take a thyroid tablet, a dose that is too high. A mildly low TSH with normal T3 and T4 often needs only a repeat. TSH can also be low in early pregnancy, during serious illness, and with steroid tablets.
Usually nothing to worry about when
It is between the top of the range and about 10, free T4 is normal, you feel well and you are not pregnant or planning pregnancy: repeat it in 6–12 weeks. A TSH just below the range with normal T3 and T4 is also usually just repeated.
See a doctor when
Within a week or two if TSH is above 10, or high with a low free T4. This week if you are pregnant or trying for a baby and TSH is above about 4, or above the pregnancy range printed on your report, even when the lab’s usual range goes higher. This week if TSH is low with a racing or irregular heartbeat, weight loss, tremor, or if you are over 60.

Free T3 (FT3)

The active hormone that is free, not bound to proteins: the part the body can use

Typical adult range About 2.0–4.4 pg/mL (or 3.5–7.8 pmol/L, depending on the lab)

High usually means
Usually an overactive thyroid, especially with a low TSH. Mostly used to judge how overactive it is.
Low usually means
Very often due to illness, fasting or poor eating rather than thyroid disease, when TSH is normal.
Usually nothing to worry about when
It is mildly low and TSH and free T4 are normal.
See a doctor when
This week if it is high with a low TSH.

Free T4 (FT4)

The free part of thyroxine; a more reliable guide than total T4

Typical adult range About 0.8–1.8 ng/dL (or 9–25 pmol/L, depending on the lab)

High usually means
With a low TSH, an overactive thyroid. In people taking a thyroid tablet, it can read slightly high if blood is taken soon after the morning dose; TSH is the better guide then.
Low usually means
With a high TSH, an underactive thyroid that usually needs treatment. A low free T4 with a low or normal TSH is unusual and needs a doctor to look at the pituitary gland.
Usually nothing to worry about when
It is just outside the range and TSH is normal.
See a doctor when
Within a week or two if it is low with a high TSH, or high with a low TSH. This week if both free T4 and TSH are low.

Anti-TPO (thyroid peroxidase antibodies)

Antibodies against the thyroid: a sign the body’s own defences are reacting to it

Typical adult range Below the lab’s cut-off, often about 35 IU/mL

High usually means
Points to autoimmune thyroid disease, most often Hashimoto’s thyroiditis. With a mildly high TSH, positive antibodies make it more likely that the thyroid will slowly become underactive over the years. Positive antibodies are also found in many people whose thyroid works normally.
Usually nothing to worry about when
It is positive but TSH and free T4 are normal: nothing to treat, just a TSH check about once a year, or if you feel unwell. The antibody level itself does not need repeating.
See a doctor when
This week if you are pregnant or planning a pregnancy and it is positive, so TSH can be checked and kept in range.

Results that go together.

PatternsTypical, not certain
When you seeIt usually means
High TSH, normal free T4Subclinical (mild) hypothyroidism. Usually repeat in 6–12 weeks. Treatment is usually considered when TSH stays above 10, or sooner if you are pregnant or trying for a baby. Positive anti-TPO makes it more likely to progress.
High TSH, low free T4An underactive thyroid (hypothyroidism). Usually needs a daily tablet, and TSH is checked 6–8 weeks after starting. It can also raise cholesterol and cause tiredness and weight gain.
Low TSH, high free T4 or free T3An overactive thyroid (hyperthyroidism). Needs a doctor within a week or two, sooner with a racing heart. See thyroid problems.
Low TSH, normal free T4 and free T3Subclinical (mild) overactivity, or a thyroid tablet dose that is a little high. Usually repeated in 6–12 weeks; it matters more in people over 60 because of the heart rhythm and bones.
Normal TSH, high total T4 or total T3Often pregnancy or the contraceptive pill raising the carrier proteins. Free T4 is usually normal. Not a thyroid disease.
Low TSH and low free T4Unusual. Can follow a serious illness, or point to a problem with the pituitary gland. See a doctor this week.

Get help today if

  • Known overactive thyroid with high fever, a very fast heartbeat, confusion, vomiting or loose motions: go to hospital today, or call 112.
  • Fever, sore throat or mouth ulcers while taking carbimazole or a similar anti-thyroid tablet: stop the tablet and get a blood count today. These medicines can rarely lower the white cells that fight infection.
  • Very underactive thyroid with marked drowsiness, confusion, feeling very cold or slow breathing, especially in an older person: go to hospital today, or call 112.
  • A racing or irregular heartbeat with chest pain, breathlessness or fainting, and a low TSH: go to hospital today, or call 112 if the chest pain lasts more than a few minutes or you faint.

Call 112 or go to the nearest emergency department. Ambulance: 108 (102 in some states).

Read more.

Questions people ask.

  1. My TSH is 5.5. Do I need a thyroid tablet?

    Usually not straight away. With a normal free T4, a TSH of 5.5 is mild. TSH can rise after an illness and often settles. A repeat in 6–12 weeks, with free T4 and anti-TPO, is the usual next step. If you are pregnant or trying for a baby, see a doctor this week, as the targets are tighter.

  2. Do I need to fast for a thyroid test?

    No. Food does not change TSH much. If you take a thyroid tablet, keep to your usual routine, and tell the lab about any biotin or hair-and-nail supplement, which can upset the result.

  3. What is anti-TPO positive?

    It means your body’s defences are reacting to the thyroid, most often from Hashimoto’s thyroiditis. If TSH is normal, nothing needs treating. It does make an underactive thyroid more likely in future, so check TSH about once a year, and during pregnancy.

  4. Which is more important, T3, T4 or TSH?

    TSH, for most people. It is the most sensitive sign of a thyroid that is working too slowly or too fast. Free T4 then shows how much hormone is actually in the blood. T3 is most useful for an overactive thyroid.

Where this can be checked

These are trusted general sources. The advice on this page is Dr. Arya’s, written for patients in India. Ranges differ between labs: go by the range printed on your own report.

Your whole report, read by your doctor.

Send every page, old reports too. He reads them himself and tells you what changed and what to do.

Send your report for ₹199

Dr. Prabhat Arya · MBBS, MD (Internal Medicine)