# Thyroid profile: what TSH, T4, and T3 mean

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TSH, free T4, free T3, and TPO antibodies, read as one picture of the thyroid axis rather than four separate numbers.

This is the Markdown version of https://doctano.com/panels/thyroid-profile. The HTML page is the canonical version.

A thyroid profile groups tests that describe the thyroid axis: TSH, free T4, free T3, and sometimes TPO antibodies. TSH is the pituitary signal, and free T4 and free T3 are the hormones it regulates. This page explains what each line reflects, not whether your values are normal. The range printed on your report is the one that applies.

A thyroid profile is ordered when a clinician wants to see how the thyroid axis is working, and it appears in many checkup packages. The lines answer different questions: a pituitary signal, two circulating hormones, and a marker of autoimmune activity.

## What the panel measures

The thyroid gland produces thyroxine, known as T4, and triiodothyronine, known as T3. Most T3 in the body is converted from T4 in other tissues rather than made in the gland. Both hormones travel in blood largely bound to carrier proteins, and the unbound portion is the part available to tissues. Free T4 and free T3 measure that fraction.

TSH is made by the pituitary and prompts the thyroid to produce hormone. It is the pituitary's side of the conversation, and often the first thyroid line a clinician reads because it responds to what the gland is producing.

TPO antibodies are not a hormone measurement. They are antibodies against thyroid peroxidase, an enzyme involved in making thyroid hormone, and they are an autoimmune marker. The panel therefore combines a regulatory signal, two hormone measurements, and a marker of immune activity.

## The tests inside it

| Test | Also printed as | Unit | What it reflects |
| --- | --- | --- | --- |
| [TSH](https://doctano.com/tests/tsh) | Thyrotropin, thyroid-stimulating hormone | mIU/L (uIU/mL) | The pituitary signal that prompts the thyroid gland to produce hormone. |
| [Free T4](https://doctano.com/tests/free-t4) | FT4, free thyroxine | ng/dL, pmol/L | The unbound portion of thyroxine, the main circulating thyroid hormone. |
| [Free T3](https://doctano.com/tests/free-t3) | FT3, free triiodothyronine | pg/mL, pmol/L | The unbound portion of triiodothyronine, the hormone that acts on tissues. |
| [TPO antibodies](https://doctano.com/tests/tpo-antibodies) | Anti-TPO, thyroid peroxidase antibody | IU/mL, assay-dependent | Antibodies against thyroid peroxidase, an autoimmune marker rather than a hormone value. |

Some reports also print total T4 or total T3, which measure bound and free hormone together and are different tests from the free values.

## Why this page does not print a range

Thyroid reference ranges are not universal. Laboratories build them from their own methods and populations, and the TSH range can differ with age and pregnancy. Antibody assays vary even more, because one platform may report a number while another reports a qualitative result, and the threshold belongs to that assay.

The range printed on the report that produced your value is the one that applies. Doctano keeps that printed range with the result. It does not replace it with a general range from the internet, because the same number can mean different things in different methods and people.

## What moves together

TSH and free T4 are linked by a feedback loop. When the gland produces less hormone, the pituitary tends to raise its signal, and when it produces more, the signal tends to fall. That is why the two lines are read together.

Free T3 adds the hormone that acts on tissues. Because most T3 is converted from T4 outside the gland, free T3 does not always track free T4 exactly. Conversion can be affected by illness and by some medicines.

TPO antibodies can be present without thyroid disease, and their absence does not rule a thyroid problem out. They are a marker of autoimmune activity, not a measure of how much hormone the gland is making. A positive antibody result alongside unusual hormone values is a pattern for a clinician, not a diagnosis.

## How to read the report's own grouping

- **Read the order.** Many reports print TSH, free T4, and free T3, then TPO antibodies. Some put the hormones first. The order does not change what is measured.
- **Find the flags.** A flag means the laboratory compared the value with its printed range. It may be high, low, or a written comment, and it is not a diagnosis.
- **Check which values are calculated.** A free T4 index, a T3 uptake, or a ratio can be derived from other measurements. They are not the same tests as free T4 and free T3.
- **Check the unit.** mIU/L and uIU/mL describe the same scale for TSH. ng/dL and pmol/L are different scales for free T4, and pg/mL and pmol/L for free T3. Convert before comparing.
- **Check the timing.** TSH is released in pulses and can vary through the day. Pregnancy changes the axis, and acute illness can move thyroid results.
- **Read the remarks.** The method name, an assay note, or an interference comment can explain a result that looks out of place.

## What a flagged result means, and what it does not

A flag means the value sits outside the range the laboratory printed. It is a prompt to look at the other lines, not a diagnosis. TSH and free T4 in opposite directions is a pattern a clinician interprets with history and examination.

A value inside the printed range is not proof that nothing is wrong. Ranges describe a reference group, and a person can have symptoms or a changing trend while values sit inside the printed interval. The trend and the other lines carry information a single flag does not.

## The cross-year view

Compare the same test, in the same unit, from the same laboratory where possible. TSH in mIU/L and uIU/mL is the same scale. Free T4 in ng/dL and pmol/L is not, and a change of unit can look like a change in the result. Antibody results from different assays may not be comparable at all.

TSH can move between samples without a change in the gland, so a single difference is weaker evidence than a consistent direction across several reports.

Doctano keeps each result with its printed range and places it on the profile's timeline. Names and units are normalized across laboratories, so the same marker lines up across years, and every point still opens the report it came from.

## What this page is not

This page explains the panel in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the values and units against the original report, and discuss the result with a qualified professional.

## Thyroid profile questions

**What does a thyroid profile include?**

Most thyroid profiles include TSH, free T4, and free T3. Some add TPO antibodies, and some laboratories also print total T4 or total T3. The exact set depends on what was ordered, and the report lists the tests it contains.

**Why is TSH read with free T4 and free T3?**

TSH is the pituitary signal that prompts the thyroid gland. Free T4 and free T3 are the hormones the gland produces. Reading them together shows the signal and the response, but the pattern is not a diagnosis on its own.

**Can TPO antibodies be present without thyroid disease?**

Yes. TPO antibodies can be present in people with no thyroid problem, and their absence does not rule one out. The result is read with TSH, the thyroid hormones, and the person's history.

**Why does this page not give a thyroid range?**

Reference ranges differ by laboratory, method, age, sex, and pregnancy, and some laboratories print method-specific ranges. The range printed on your report is the one that applies, and Doctano keeps that printed range with the result.

## Limits

**This is not a diagnosis.** A thyroid profile is read with your history, your medicines, and the range printed on your report. Verify the values against the original report and discuss them with a qualified professional.

## Links

- [Homepage](https://doctano.com/)
- [Lab report tracker](https://doctano.com/lab-report-tracker)
- [All panels](https://doctano.com/panels/)
- [TSH](https://doctano.com/tests/tsh)
- [Free T4](https://doctano.com/tests/free-t4)
- [Free T3](https://doctano.com/tests/free-t3)
- [TPO antibodies](https://doctano.com/tests/tpo-antibodies)
- [Kidney function test](https://doctano.com/panels/kidney-function-test)
- [Iron studies](https://doctano.com/panels/iron-studies)
- [Reference ranges](https://doctano.com/guides/reference-ranges)
- [All guides](https://doctano.com/guides/)