Thyroid test: TSH, fT4 and fT3
Your thyroid partly sets the pace of your metabolism. If it runs slower or faster you notice it in your energy, weight, temperature and mood. Three values together give a usable picture of that.
TSH is the hormone your pituitary uses to drive the thyroid. It is an indirect measure: if TSH rises, the pituitary is having to push harder. That is why TSH is often measured first, and sometimes as the only value.
That last part is the problem. TSH moves over the day, shifts during illness and stress, and can be normal while the thyroid hormones themselves sit at the edge. fT4 is the hormone the thyroid makes, fT3 is the active form your cells use. Some people convert fT4 into fT3 less well, and you only see that if fT3 is measured too.
Which thyroid values do you need?
Message what you are noticing and whether TSH was measured before. Mario will say whether TSH with fT4 and fT3 is enough, or whether adding more makes sense.
Reachable Monday to Saturday, 08:00 to 18:00. An appointment can usually be scheduled within a few days.
When to measure this
- With persistent fatigue that does not improve with sleep.
- With unexplained weight change in either direction.
- If you feel cold or hot compared to others around you.
- With slow bowel movements, dry skin or hair loss.
- With palpitations, restlessness or poor sleep.
- If thyroid problems run in your family.
What is actually drawn
In the Hormones and Stress package these three sit alongside the sex hormones, SHBG, prolactin, DHEA-S and morning cortisol.
Preparation
No fasting needed. Draw in the morning where possible, and at roughly the same time for a follow-up, because TSH moves over the day. If you take thyroid medication, take it after the draw and state which medication and dose you use. High-dose biotin can interfere with the assay, so pause it for a few days in consultation.
Which package includes this
Measuring this marker on its own is possible too. All three values are determined together, because TSH alone gives an incomplete picture. For reference, providers with a collection point typically charge 59 to 69 euro for a single marker, and you travel there yourself.
These are the actual amounts. The lab cost is what the lab charges, passed on without a markup. There is no discounted-from price and no subscription. Enter your address in the price calculator for the exact total including travel.
What your result means
The combination of the three tells you more than any one of them. A raised TSH with a normal fT4 reads differently from a raised TSH with a lowered fT4. You get an explanation per value plus how they relate.
A blood test does not establish a thyroid condition. If the values point that way, that is reason to see your GP, who can add antibodies or an ultrasound.
On the difference between a lab reference and a target range, see this article. If you feel unwell while your value sits inside the reference, read this one.
Frequently asked questions
Is TSH on its own enough?
Usually not.
TSH is an indirect measure and can be normal while fT4 or fT3 sits at the edge. fT3 in particular is rarely drawn as standard, yet it is the active form your cells use.
Do I need to fast for a thyroid test?
No.
It does help to draw in the morning and to keep the same time for a follow-up, because TSH moves over the day.
I take thyroid medication. When do I draw?
Before your daily dose.
Taking the medication first means you measure a peak rather than your usual level. Always state which medication and dose you use.
Can a supplement affect my result?
Yes, high-dose biotin can.
Biotin is common in hair and nail supplements and can interfere with the assay. Pause it for a few days before the draw in consultation.
What if my values sit just inside the reference?
That is neither proof that nothing is wrong nor a diagnosis.
It is a reason to repeat over time and to discuss your symptoms with your GP. See this article.
Note: a blood test gives you insight and direction. It does not prove or rule out a condition on its own. Results are meant for prevention and for tracking change over time, not as a diagnosis. For symptoms or values outside the reference range, see your GP.