Blood Testing · Coming Soon
Thyroid
Function Test
One of the most frequently requested tests in general practice. A Thyroid Function Test checks whether your thyroid gland is producing the right amount of hormone — with results that can explain fatigue, weight changes, mood shifts, and more. Coming soon to The GP Service.
Licensed UK clinicians
Results within 24 hours
Clinician-reviewed results
Overview
What Is a Thyroid Function Test?
A Thyroid Function Test (TFT) is a blood test that measures the hormones produced by your thyroid gland and the pituitary signal that controls it. The thyroid — a butterfly-shaped gland at the front of your neck — regulates your body's metabolism, energy production, heart rate, body temperature, mood, and much more. When it produces too much or too little hormone, the effects ripple across virtually every system in the body.
The test measures TSH (thyroid-stimulating hormone), which is produced by the pituitary gland and tells the thyroid how much hormone to make, alongside the thyroid hormones themselves: free T4 (thyroxine) and often free T3 (triiodothyronine). Together, these values reveal whether the thyroid is underactive (hypothyroidism), overactive (hyperthyroidism), or functioning normally — and can identify early or subclinical dysfunction before symptoms become severe.
It is one of the most commonly requested tests in general practice, and for good reason. Thyroid disorders affect an estimated 1 in 20 people in the UK, are significantly more common in women, and are frequently missed or misattributed — particularly in their early stages — because their symptoms overlap with conditions such as depression, anxiety, chronic fatigue, and menopause.
Coming Soon to The GP Service
We are launching Thyroid Function Testing shortly — including clinician-reviewed results, a plain-English explanation of your TSH, T4 and T3 values, and onward management including medication and specialist referral where needed. Register above to be notified as soon as it goes live.
What Gets Measured
What Does a Thyroid Function Test Include?
A standard TFT measures TSH as the primary screening marker, usually alongside free T4. A more comprehensive panel adds free T3, and extended panels can include thyroid antibodies (TPO and TgAb) to investigate autoimmune thyroid disease. Here is what each marker tells you.
TSH
Normal: 0.4–4.0 mU/L
Thyroid-stimulating hormone — produced by the pituitary gland. The most sensitive marker of thyroid function. A high TSH means the pituitary is working hard to stimulate an underactive thyroid. A low TSH means the thyroid is overactive or being over-treated.
Thyroid-stimulating hormone — produced by the pituitary gland. The most sensitive marker of thyroid function. A high TSH means the pituitary is working hard to stimulate an underactive thyroid. A low TSH means the thyroid is overactive or being over-treated.
mU/L
Free T4
Normal: 9–23 pmol/L
The inactive form of thyroid hormone — thyroxine — made directly by the thyroid gland. Converted to the active T3 form in tissues. Low free T4 alongside a high TSH confirms primary hypothyroidism. High free T4 with a low TSH points to hyperthyroidism.
The inactive form of thyroid hormone — thyroxine — made directly by the thyroid gland. Converted to the active T3 form in tissues. Low free T4 alongside a high TSH confirms primary hypothyroidism. High free T4 with a low TSH points to hyperthyroidism.
pmol/L
Free T3
Normal: 3.5–7.8 pmol/L
The active thyroid hormone — triiodothyronine — that acts directly on cells and tissues. Important in monitoring those on levothyroxine who continue to experience symptoms despite normal TSH and T4, and in diagnosing T3-toxicosis. Not always included in a standard panel.
The active thyroid hormone — triiodothyronine — that acts directly on cells and tissues. Important in monitoring those on levothyroxine who continue to experience symptoms despite normal TSH and T4, and in diagnosing T3-toxicosis. Not always included in a standard panel.
pmol/L
TPO Antibodies
Normal: <34 IU/mL
Thyroid peroxidase antibodies — a marker of autoimmune thyroid disease. Elevated in Hashimoto's thyroiditis (the most common cause of hypothyroidism) and Graves' disease. Included in extended panels when autoimmune thyroid disease is suspected.
Thyroid peroxidase antibodies — a marker of autoimmune thyroid disease. Elevated in Hashimoto's thyroiditis (the most common cause of hypothyroidism) and Graves' disease. Included in extended panels when autoimmune thyroid disease is suspected.
IU/mL
TgAb
Normal: <115 IU/mL
Thyroglobulin antibodies — another autoimmune marker. Elevated levels alongside TPO antibodies strongly support a diagnosis of Hashimoto's thyroiditis. Also used in monitoring thyroid cancer after treatment.
Thyroglobulin antibodies — another autoimmune marker. Elevated levels alongside TPO antibodies strongly support a diagnosis of Hashimoto's thyroiditis. Also used in monitoring thyroid cancer after treatment.
IU/mL
Reverse T3
Normal: 10–24 pmol/L
An inactive form of T3 produced in elevated amounts during illness, extreme stress, or severe caloric restriction. Not included in standard TFTs but relevant in specialist evaluation of persistent symptoms despite normal TSH and T4 values.
An inactive form of T3 produced in elevated amounts during illness, extreme stress, or severe caloric restriction. Not included in standard TFTs but relevant in specialist evaluation of persistent symptoms despite normal TSH and T4 values.
pmol/L
Results Always Need Clinical Context
TSH has natural variation within individuals over time, and what is "normal" for the population may not be optimal for you. Results are most meaningful when interpreted alongside your symptoms, medical history, and any medications you are taking. When we launch TFT testing, every result comes with a clinician review — not just a printout of numbers against a range.
Indications
When Do You Need a Thyroid Function Test?
Thyroid disorders are common and frequently underdiagnosed. The symptoms span a wide range and overlap significantly with other conditions, which is why a TFT is appropriate in many different situations — both to investigate new symptoms and to monitor known thyroid disease.
Persistent Fatigue
Unexplained tiredness that doesn't improve with rest is one of the most common presentations of hypothyroidism — the thyroid isn't producing enough hormone to keep your energy metabolism running properly.
Unexplained Weight Changes
Gaining weight despite no change in diet or activity can suggest hypothyroidism. Losing weight without trying, especially with a good appetite, can be a sign of hyperthyroidism.
Mood or Cognitive Symptoms
Depression, anxiety, brain fog, and poor concentration are all associated with thyroid dysfunction. A TFT should be considered before or alongside mental health treatment in many cases.
Intolerance to Cold or Heat
Feeling unusually cold all the time points to hypothyroidism. Feeling excessively hot and sweaty, or heat intolerance, is more characteristic of hyperthyroidism or thyrotoxicosis.
Heart Rate Changes
A slow heart rate (bradycardia) may indicate hypothyroidism. A fast or irregular heart rate — especially with palpitations — can be caused by an overactive thyroid, including atrial fibrillation in older patients.
Monitoring Levothyroxine
If you are on levothyroxine for hypothyroidism, regular TFTs are essential to ensure your dose is keeping your TSH within your optimal range. Many patients on treatment still experience symptoms due to suboptimal dosing.
Pregnancy Planning or Pregnancy
Thyroid disease in pregnancy carries significant risks to mother and baby. TSH is routinely tested in those with thyroid disease who are pregnant or planning to conceive, and targets are tighter than for the general population.
Menstrual Irregularities
Both hypothyroidism and hyperthyroidism can disrupt the menstrual cycle — causing heavy periods, irregular cycles, or periods stopping altogether. A TFT is part of a standard investigation for menstrual problems.
Routine Health Screening
A TFT as part of a general health check can identify subclinical thyroid disease — where TSH is abnormal but symptoms are absent or mild — before it progresses to overt dysfunction.
The Process
What's Involved in Getting a TFT
A Thyroid Function Test requires only a small blood sample and takes just a few minutes. Here is what the process will look like from booking to receiving your results — as it will work when we launch this service.
1
Book Your Test
Request a TFT online in minutes — no GP referral needed.
Choose a convenient phlebotomy location
Or request a home visit blood draw
Morning appointments recommended for optimal TSH accuracy
2
Give Your Sample
A simple venous blood draw — typically less than 5 minutes.
Take any thyroid medication after, not before, the draw
Processed by an accredited UK laboratory
Results typically within 24–48 hours
3
Review with a Clinician
Your results are reviewed by a licensed clinician, not just sent as a data file.
Plain-English explanation of TSH, T4 and T3
Abnormal values explained in clinical context
Prescriptions and referrals arranged where needed
Launching Shortly
We are finalising our laboratory partnerships and clinical workflow for Thyroid Function Testing. We expect to launch within the coming weeks. Register at the top of this page to be notified as soon as it is available — early registrants will receive priority access.
Interpreting Results
What Can an Abnormal TFT Tell You?
The pattern of TSH, free T4, and free T3 values together tells a more complete story than any single marker alone. Here are the most common patterns and what they typically indicate.
Pattern
What It Suggests
Common Causes
High TSH + low free T4
Overt hypothyroidism
Hashimoto's thyroiditis, post-thyroidectomy, radioiodine treatment, iodine deficiency
High TSH + normal free T4
Subclinical hypothyroidism
Early Hashimoto's, iodine deficiency, medication side effects
Low TSH + high free T4
Overt hyperthyroidism
Graves' disease, toxic multinodular goitre, thyroiditis
Low TSH + normal free T4
Subclinical hyperthyroidism
Early Graves', autonomous thyroid nodule, excess levothyroxine
Normal TSH + low free T4
Central hypothyroidism
Pituitary or hypothalamic dysfunction — rare but important to exclude
Normal TSH + symptoms persisting
May require extended panel
Poor T4→T3 conversion, low free T3, elevated reverse T3, autoimmune disease
Elevated TPO antibodies
Autoimmune thyroid disease
Hashimoto's thyroiditis (hypothyroid) or Graves' disease (hyperthyroid)
A Single TSH Value Is a Starting Point, Not a Complete Picture
TSH alone doesn't tell the whole story. Many people with hypothyroid symptoms have TSH values that fall within the "normal" range but are not optimal for them as individuals. When we launch this service, our clinicians will interpret your results in the context of your symptoms and history — not just compare a number to a population range.
Conditions
Hypothyroidism vs Hyperthyroidism
The two main categories of thyroid dysfunction sit at opposite ends of the spectrum — one where the thyroid produces too little hormone, and one where it produces too much. Understanding the difference helps contextualise your results and what treatment might look like.
Hashimoto's Thyroiditis
Graves' Disease
Toxic Multinodular Goitre
Postpartum Thyroiditis
Thyroid Nodules
Subacute Thyroiditis
Secondary Hypothyroidism
Thyroid Cancer Monitoring
Hypothyroidism — Underactive Thyroid
Hypothyroidism occurs when the thyroid gland does not produce enough T4 and T3 to meet the body's needs. The pituitary responds by increasing TSH — which is why a raised TSH is the first indicator. The most common cause in the UK is Hashimoto's thyroiditis, an autoimmune condition where the immune system gradually damages thyroid tissue. Symptoms develop slowly and are often mistaken for other conditions: fatigue, weight gain, feeling cold, constipation, dry skin, low mood, brain fog, and slow heart rate. Treatment is levothyroxine — a synthetic T4 that the body converts to the active T3.
Hyperthyroidism — Overactive Thyroid
Hyperthyroidism occurs when the thyroid produces excess hormone, suppressing TSH to very low or undetectable levels. Graves' disease — another autoimmune condition — is the most common cause. Symptoms reflect an accelerated metabolism: weight loss despite a good appetite, heat intolerance, palpitations, tremor, anxiety, loose stools, and sometimes a visible swelling of the neck (goitre) or eye changes (in Graves' disease). Treatment options include antithyroid medications (carbimazole), radioiodine therapy, or thyroid surgery, depending on cause and severity.
Already Have a Thyroid Diagnosis?
You don't need to wait for our TFT service to launch if you already have thyroid results you need reviewed, a prescription that needs adjusting, or symptoms you're unsure about. Our clinicians can review existing results and manage thyroid conditions as part of a general health consultation, available now. Book a consultation
Why The GP Service
What Will Make Our TFT Service Different
Private thyroid testing in the UK ranges from a basic TSH-only result posted to you as a PDF, to genuinely comprehensive panels with clinical interpretation. We are building the latter. Here is what will set our Thyroid Function service apart.
Every result reviewed by a licensed clinician
Your TFT will not be returned as a raw data file. A licensed UK clinician will review your TSH, T4, and T3 values in the context of your symptoms and history before your results reach you.
Plain-English explanations, not just numbers
TSH of 4.8 mU/L means very little without context. We will tell you what your results mean for you — not just whether they sit inside a population reference range.
Comprehensive panels available
TSH alone is not always enough. We will offer panels including free T4, free T3, and thyroid antibodies — so you get a complete picture rather than a single data point.
Prescriptions issued same day where appropriate
If your results indicate that levothyroxine, carbimazole, or another thyroid medication is needed, our clinicians can prescribe in the same consultation. No second appointment, no waiting room.
Ongoing monitoring supported
Thyroid conditions require regular retesting. We will support ongoing monitoring — adjusting medication doses based on results and symptoms, not just keeping TSH inside a population reference range.
Joined up with your NHS care
We share results and clinical notes with your NHS GP where you consent. Our service complements your existing care — particularly valuable if you are waiting for an NHS endocrinology appointment.
Our Clinical Approach
How We Will Approach Your TFT Results
A TSH outside the reference range is the beginning of a clinical conversation, not the end of one. Here is what the process will look like from the moment your sample is taken to any onward management being arranged.
You book and give your sample
Select a phlebotomy location or request a home blood draw. Morning appointments are preferred for the most accurate TSH reading. If you are on levothyroxine, take your medication after the draw. The appointment typically takes under 10 minutes.
Laboratory analysis — results within 24–48 hours
Your sample is processed by a CQC-registered UK laboratory. TSH, free T4, and free T3 (or the panel you selected) are analysed and passed to your reviewing clinician.
Clinician reviews every value in context
A licensed clinician reviews your results alongside your reason for testing, current symptoms, any medications, and relevant history. TSH is not assessed in isolation — the full picture matters.
You receive a plain-English results summary
Your results are returned with a written explanation of every significant value. Normal results are confirmed clearly. Any values outside the reference range are explained — what they suggest, how clinically significant the deviation is, and what the likely causes are.
Treatment arranged where needed
If your results indicate that levothyroxine, antithyroid medication, or further investigation is appropriate, we arrange this directly. You will not be told your TSH is abnormal and left to figure out the next step on your own.
Results shared with your NHS GP
With your consent, your results and the associated clinical note are shared with your NHS GP, so they are part of your complete health record. If your results are clinically significant, we will flag these proactively.
What If I Already Have FBC Results I Don't Understand?
You do not need to wait for our FBC service to launch if you already have blood results you want reviewed. Our clinicians can discuss existing results — from your NHS GP, a previous private test, or a hospital appointment — as part of a general health consultation, available now. Book a consultation
In the Meantime
What to Do While the Service Launches
If you are here because you are experiencing symptoms and need answers now, you do not have to wait. There are several routes available to you today through The GP Service, alongside registering for early access to our TFT.
Book a General Health Consultation
A licensed clinician can review your symptoms, advise on what testing is appropriate, and arrange a private blood test referral today — including a TFT if clinically indicated.
Get Existing Results Reviewed
Already have TFT results from your GP or a previous test but unsure what they mean? Book a consultation to have a clinician interpret every value and advise on next steps.
Request a Private Blood Test Referral
If you need a thyroid test but cannot get an NHS appointment, our clinicians can issue a private laboratory referral for TSH, T4, T3, and antibodies today.
Levothyroxine Dose Review
If you are on thyroid medication but still experiencing symptoms, our clinicians can review your current dose and arrange repeat testing to optimise your treatment — without waiting for the full TFT service to launch.
Register for Early Access
Leave your details at the top of this page and we will notify you the moment TFT testing goes live — including any introductory pricing available to early registrants.
Thyroid Function Testing — coming to The GP Service soon.
Register now and be the first to know when we launch. Our TFT service will include a clinician-reviewed result, a plain-English explanation of your TSH, T4 and T3, and onward management if anything needs following up — all without a waiting room.
Register for Early Access
Morning appointments available
Results within 24–48 hours
Clinician-reviewed — not just a data file
Secure & confidentiaL
Licensed UK clinicians
Frequently Asked Questions
What does a Thyroid Function Test measure?
A standard TFT measures TSH (thyroid-stimulating hormone), free T4 (thyroxine), and often free T3 (triiodothyronine). TSH is produced by the pituitary gland and is the most sensitive marker of thyroid activity — it rises when the thyroid is underactive and falls when it is overactive. Free T4 and free T3 measure the hormones produced by the thyroid gland itself. Extended panels can also include thyroid antibodies (TPO and TgAb) to investigate autoimmune thyroid disease.
Do I need to fast before a Thyroid Function Test?
Fasting is not strictly required for a standard TFT, but there are two timing considerations worth knowing. First, TSH shows natural diurnal variation — it is highest in the early morning and lower in the afternoon, so morning samples give the most consistent results. Second, if you take levothyroxine, you should take your dose after your blood draw rather than before — taking it beforehand can temporarily elevate your free T4 and lead to an inaccurate picture of your baseline levels.
How quickly do Thyroid Function Test results come back?
Results from a private laboratory are typically available within 24–48 hours of the sample being received. NHS results usually take 2–5 working days. When we launch this service, we aim to return results with a clinician review within 24–48 hours of your sample reaching our accredited laboratory.
My TSH is in the normal range but I still feel unwell — what does that mean?
This is one of the most common scenarios we see. The TSH reference range (typically 0.4–4.0 mU/L) is based on population data, and many clinicians argue that the optimal TSH for most people is actually in the lower half of that range. Additionally, some people with a normal TSH have a suboptimal conversion of T4 to the active T3, which a standard test may not detect. An extended panel including free T3 and thyroid antibodies can provide more information in this situation. Our clinicians will assess your results in the context of your symptoms — not just compare a number to a reference interval.
What happens if my results are abnormal?
All results — normal or abnormal — will be reviewed by a licensed clinician before being returned to you. If your TSH or other values are outside the reference range, your clinician will explain what the finding means in the context of your symptoms, whether any further tests are needed, and whether treatment or referral is appropriate. For hypothyroidism, this will typically mean a levothyroxine prescription issued in the same consultation. For hyperthyroidism, further investigation and, where appropriate, carbimazole or specialist referral. You will never receive an abnormal result without clinical support.
Can I get a thyroid test without seeing a GP first?
Yes — when this service launches, you will be able to request a TFT directly through The GP Service without a prior GP appointment or referral. Our clinicians will review your results and discuss them with you directly. If your results indicate something requiring specialist referral or liaison with your NHS GP, we will manage that on your behalf.
I'm already on levothyroxine — can I use this service to monitor my treatment?
Yes — ongoing thyroid monitoring for people on levothyroxine is one of the most common uses of a private TFT. Many patients on treatment have TSH values that sit within the reference range on paper but are not optimal for them, or they have free T3 levels that are not being picked up by a basic TSH-only test. When we launch, we will support ongoing monitoring with dose optimisation based on your full panel and symptoms — not just a tick-box check that your TSH is inside the reference interval.
Will my results be shared with my NHS GP?
With your consent, yes. We strongly encourage sharing results and any associated clinical notes with your NHS GP so that your full health picture is available to whoever provides your care. If any findings are particularly significant, our clinicians will advise you on the importance of informing your NHS GP and can write to them directly if appropriate.
When is this service launching?
We expect to launch Thyroid Function Testing shortly. Register at the top of this page to be notified as soon as it goes live. Early registrants will receive priority access and will be informed of any introductory pricing before it is made public.
Medical Disclaimer: The information on this page is provided for educational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare professional with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay seeking it because of something you have read on this page. If you think you may have a medical emergency, call 999 or your local emergency services immediately.