Thyroid function test
A private thyroid blood test to check hormones involved in metabolism, energy, temperature regulation and weight change.
Book a GP blood test appointment if you have symptoms of an overactive or underactive thyroid, or want previous thyroid results reviewed.
Test options
Thyroid function blood test
Use the options below if you already know which test you need. If you are unsure, book a GP blood test appointment and your GP can advise.
TSH
Free T4
TSH
T4
TSH
Free T3
Free T4
Thyroglobulin Abs
Thyroid Peroxidase
Free T3
Free T4
TSH
From booking to results
Your appointment, step by step
Book online, see a GP, have your sample taken during the appointment and view your results securely in your DocTap account.
- 1Book online in minutesChoose your preferred clinic and time, and select a male or female clinician where available. You will get instant confirmation.
- 2We will tell you how to prepareMost blood tests do not need fasting. If a test needs anything specific beforehand, we will let you know before your appointment.
- 3See a GP and have your sample takenYour appointment includes a 15-minute GP consultation to discuss symptoms, check suitability or advise which test you need. A quick blood sample is then taken from your arm.
- 4Get results and follow-upYou will get a message when your result is ready. Your results and doctor's report will be available securely in your DocTap account; abnormal results are prioritised and your clinician will contact you if urgent action is needed.
What it can show
What a thyroid function test tells you
Thyroid results help show whether your thyroid is broadly underactive, overactive or in range.
TSH is usually the starting point
TSH is a hormone from the brain that signals the thyroid. If the thyroid is underactive, TSH often rises. If the thyroid is overactive, TSH is often low. This is why TSH is usually the first marker doctors look at.
T4 and sometimes T3 add detail
Free T4, and sometimes Free T3, show thyroid hormone levels in the blood. These help your GP understand whether a TSH change is likely to represent an underactive or overactive thyroid pattern.
Symptoms can overlap with many conditions
Tiredness, weight change, anxiety, low mood, palpitations and temperature sensitivity can all have causes outside the thyroid. The blood test helps decide whether thyroid function is likely to be part of the explanation.
When to test
When thyroid testing is worth doing
Thyroid testing is most useful when symptoms fit a pattern or you need to monitor a known thyroid issue.
Possible underactive thyroid symptoms
Testing may be useful if you have persistent tiredness, weight gain, feeling cold, constipation, dry skin, hair changes, low mood or sluggishness, especially if symptoms have built up gradually.
Possible overactive thyroid symptoms
It can also help if you have palpitations, tremor, heat intolerance, sweating, anxiety-like symptoms, unexplained weight loss or changes in bowel habit. These symptoms should be discussed with a GP, especially if severe or new.
Medication or follow-up monitoring
If you already take thyroid medication, blood tests help check whether the dose still fits. Testing may also be useful after previous borderline results or where symptoms and results do not quite match.
Results
Understanding thyroid results
Thyroid results often need a trend, not just one number.
Borderline results may need repeating
A slightly abnormal TSH can sometimes settle, especially after illness or medication changes. Your GP may repeat the test before starting treatment, unless the result and symptoms clearly point in one direction.
Supplements and medicines can matter
Some medicines and supplements can affect thyroid results or lab interpretation. If you take thyroid medication, biotin, amiodarone, lithium or other regular medication, mention this during your appointment.
What may happen next
Depending on the pattern, your GP may suggest repeat thyroid tests, thyroid antibodies, medication review or referral. The aim is to match the result to symptoms rather than treating a number in isolation.
Clinical quality
The standards behind every test
The clinical standards behind every DocTap blood test, across our London clinics.
- CQC rated ‘Good’.
- Independently inspected and regulated by the Care Quality Commission.
- Fully GMC-registered doctors.
- UK-trained and experienced GPs only.
- Every consultation reviewed.
- Each one is checked for quality and safety, overseen by our Medical Director.
- No sales incentives.
- Our GPs are never paid commissions for tests or treatments.
Ready to book?
Book a GP blood test appointment, or compare prices for other blood tests.
11 locations where we test
DocTap London clinics and on-site laboratories
Canary Wharf
Situated by South Quay Footbridge, a 3-minute walk from Canary Wharf and Heron Quays stations.
Hammersmith
Situated on King Street, a 6-minute walk from Hammersmith underground stations.
Kings Cross & Euston
Located just off Euston Road, less than a 10-minute walk from both Euston and King’s Cross stations.
Liverpool Street & Bank
Located in the heart of the City, a 5-minute walk from Liverpool Street and Bank stations.
London Bridge
Located just off Borough High Street, an 8-minute walk from London Bridge station.
Bond Street
Located on Wigmore Street, just off Harley Street, a 7-minute walk from Bond Street station.
Clapham
Located on Clapham High Street, only a 3-minute walk from Clapham Common station.
Old Street
Located off Old Street, a 3-minute walk from Old Street underground station.
Stratford
Located within The Conductor building, a 6-minute walk from Stratford station, or 3 minutes from the Westfield shopping centre.
Swiss Cottage
Only a 3-minute walk from Swiss Cottage station.
Victoria
Situated on Lower Belgrave Street, a 5-minute walk from Victoria rail and underground stations.
Online GP
Speak to a GP by video or phone, wherever you are — no app needed. Ideal for follow-ups and straightforward concerns.