Home kit
Free T4 Test
Free T4, the main hormone the thyroid releases, 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 T4
Free thyroxine (FT4), one of the main thyroid hormones. It is read alongside TSH, the pituitary hormone that controls thyroid hormone production: a low TSH with a raised T3 or T4 usually points to an overactive thyroid. What counts as normal varies with age and laboratory method.
Overview
Free T4 is the main hormone the thyroid releases, and it is what a doctor looks at next once TSH is known. It is read as a pair with TSH, because the relationship between the two is what says whether a change comes from the thyroid itself or from the pituitary signal above it.
Free T4 is the unbound fraction of the main thyroid hormone, and it is what a doctor looks at next once TSH is known. The two are read as a pair, because it is the relationship between them that says whether a change is coming from the thyroid itself or from the pituitary signal above it. On its own free T4 answers half a question, so this single is most useful alongside a TSH you already have.
Who this is for and who it isn’t
Who it’s for
- Adults aged 18 and over
- Anyone adding free T4 to a TSH result they already have
- People following thyroid results over time under clinical supervision
Who it isn’t for
- Free T4 on its own answers half a question. Without TSH, a doctor cannot say much about a result either way, so this single is most useful when you already have a recent TSH. If you have neither, the Thyroid Check covers both for less than the two singles together.
- Never adjust levothyroxine on a private result; that is a decision for the clinician who prescribes 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 free T4 to a TSH result you already have
- Feeling cold, tired or gaining weight without a clear reason
- Feeling unusually hot or sweaty
- Following thyroid results over time under clinical supervision
- A clinician has asked for free T4
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 T4▼ Low
- Result
- 10.5 pmol/L
- Range
- 12–22
| Marker | Result | Units | Range | Flag |
|---|---|---|---|---|
| Free T4 | 10.5 | pmol/L | 12–22 | ▼ Low |
Doctor’s note (example)
Free T4 is just below the range. With a raised TSH this pattern is consistent with an underactive thyroid, which a doctor would usually discuss treating; with a normal TSH it is repeated first.
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 have TSH as well?
Ideally yes. TSH and free T4 are interpreted as a pair, and TSH is the more sensitive of the two, which is why a GP orders it first. The Thyroid Check includes both, and the Thyroid Check with T3 adds free T3.
Does the time of day matter?
Free T4 varies less through the day than TSH. If you are tracking results over time, keeping the sampling time roughly the same makes them easier to compare. No fasting is needed.
I am on levothyroxine. Does this show whether my dose is right?
It is one of the numbers used, but dose decisions rest on TSH, free T4 and how you feel together, and they belong with your prescriber. Follow their advice about when to sample relative to your dose.
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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