Home kit
Free T3 Test
Free T3, the active thyroid hormone, measured on its own.
- Doctor-reviewed results
- Laboratory analysis
- 1 to 2 working days from lab receipt
- No fasting required
What’s included
1 marker measured
Free T3
Free T3 (triiodothyronine) is one of the main hormones made by the thyroid, checked alongside TSH and T4 in a thyroid function test. A low TSH with high T3 and/or T4 usually points to an overactive thyroid.
Overview
T3 is the active thyroid hormone, converted from T4 inside the tissues, and free T3 measures the part that is available to act. It is most useful as an addition when TSH and free T4 have already been measured and something in the picture still does not add up.
T3 is the form of thyroid hormone that actually acts on the body, and T4 is converted into it. It is a single marker rather than a thyroid assessment: on its own it cannot say whether the thyroid is working normally, because TSH and free T4 are what the picture is built on. It is a sensible add-on when those two have already been measured, and the Thyroid Check with T3 measures all three together for less than the three singles.
Who this is for and who it isn’t
Who it’s for
- Adults aged 18 and over
- Anyone adding T3 to a TSH and free T4 they already have
- People whose clinician has asked for free T3 specifically
Who it isn’t for
- This is not a thyroid check. On its own free T3 cannot say whether your thyroid is working, because that picture is built on TSH and free T4. If this is your first thyroid test, the Thyroid Check with T3 measures all three together for less than the three singles.
- Do not change a levothyroxine dose on any private result; that belongs with the clinician who looks after it. If you have sudden chest pain that does not go away, call 999. If you have a racing or irregular heartbeat, chest pain that comes and goes, or you are losing weight without trying, contact your GP rather than waiting for a test.
- Anyone with a new, severe or worsening symptom: contact your GP or call NHS 111. A test you buy today is not a substitute for being examined.
Common reasons people choose this test
- Adding T3 to a TSH and free T4 you already have
- Feeling unusually hot or sweaty, where TSH and free T4 have already been measured
- A clinician has asked for free T3 specifically
- Following thyroid results over time under clinical supervision
- Tiredness or weight change where thyroid results so far have been unclear
These are reasons people choose to test, not signs that something is wrong. A result is one part of a picture your doctor puts together with your history and an examination.
What your result looks like
Every result is shown with the unit and the reference range exactly as the laboratory reported it, with the doctor’s note underneath.
- Free T3In range
- Result
- 4.6 pmol/L
- Range
- 3.1–6.8
| Marker | Result | Units | Range | Flag |
|---|---|---|---|---|
| Free T3 | 4.6 | pmol/L | 3.1–6.8 | In range |
Values above are examples. Your report shows your own results with the laboratory’s units and reference range for your age and sex, reviewed, signed and released by a GMC-registered doctor.
How it works
- Your kit arrivesPosted to your door, with instructions and what you need to send your sample back.
- You take your sampleFinger-prick sample at home, or a clinic blood draw, your choice
- The laboratory analyses itYour sample is processed for the measurements included in this test. Lab processing typically takes 1 to 2 working days from receipt of your sample.
- A doctor reviews and releases itA GMC-registered doctor reads every result and signs the report before it reaches you.
- Sample
- Home finger-prick kit
- Preparation
- No fasting required
- Who it's for
- Any sex · ages 18+
How to prepare
What we can and can’t tell you
The reference range beside each result is the laboratory’s own. A result in range is not a clean bill of health and a result outside it is not a diagnosis. Most ranges cover about 95% of healthy people, so about 1 in 20 healthy people fall just outside any one range. No test result replaces an examination or your own doctor’s judgement, and none of these panels is a cancer screening programme.
Read the full note
The reference range printed beside each of your results is the laboratory's own, and it is the range that applies to your result. We do not apply a second range of our own, and we do not tell you that a result the laboratory reported as normal is nonetheless too low or too high. If you see a claim elsewhere that your result ought to sit inside a narrower band than the one the laboratory printed, treat it with caution and ask your doctor.
Some assays cannot give an exact figure above or below a certain point, and those results are reported the way the laboratory sends them, for example as a value greater than a stated number. A result in range is not a clean bill of health, and a result outside a range is not a diagnosis: most reference ranges are set to cover about 95% of healthy people, so some healthy people fall just outside them. No blood test replaces an examination, a scan or your own doctor's judgement, and none of these panels is a screening programme for cancer.
If you have a symptom that is new, severe, or getting worse, contact your GP or NHS 111 rather than waiting for a test result. In an emergency call 999.
Frequently asked questions
Should I test T3 on its own?
Rarely. Free T3 means something only alongside TSH and free T4. If you have those already, this fills the gap; if you do not, the Thyroid Check with T3 is the better buy.
Does it matter what time I test?
TSH varies most through the day, and free T3 far less, but if you are following results over time it helps to sample at a similar time each go. Fasting is not needed.
I take levothyroxine. When should I take the sample?
Follow whatever your prescriber has advised about timing relative to your dose, and use the same pattern each time so results are comparable. We do not advise on dose changes.
Does biotin affect thyroid results?
It can. High-dose biotin, often found in hair and nail supplements, can make thyroid results falsely high or low. Tell us if you take it, and ask your pharmacist or GP whether to pause it before your sample.
How long do results take?
The laboratory typically takes 1 to 2 working days from receiving your sample. This does not include kit delivery, sample collection or return postage. A doctor reviews your results before they are released.
Can I choose a home kit or a clinic?
Both, it is your choice at checkout. Either collect a finger-prick sample at home with the posted kit and send it back as the instructions explain, or book a clinic appointment and have a trained clinician take the sample for you.
Is a doctor involved?
Yes. Every result is reviewed by a GMC-registered doctor who signs it off and explains what it means and what to do next.
Is it confidential?
Your results are available through your secure patient portal. Our privacy policy explains how your information is handled and when it may be shared to provide your care.
What happens to my sample and results?
Your sample is analysed at a UKAS-accredited laboratory (ISO 15189). A GMC-registered doctor then reads every result and signs the report before it is released, so nothing reaches you unreviewed. There is no option to receive results without a doctor reading them first. The report arrives in your secure portal in plain English: each result with its unit and the laboratory's own reference range, and the doctor's note on what the set means read together. If a result sits outside its range the report says so and explains what usually happens next, which is most often a conversation with your own GP, who can act on it alongside your history and examination. Most reference ranges are set to cover about 95% of healthy people, so about 1 in 20 healthy people fall just outside any one of them. On a report with many results it is common for one to sit just outside its range, and a single number on its own rarely tells the whole story. If a result needs urgent attention, the reviewing doctor is alerted straight away and we contact you by phone the same working day rather than leaving it in the portal for you to find. If a specific result needs rechecking, the reviewing doctor says so in your report.
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