Buy a thyroid function test - check TSH, free T4 and free T3

Your thyroid makes hormones that influence your metabolism, energy, body temperature and mood. When those hormones fall out of balance, you can feel it in many different ways.

A thyroid blood test can give insight into how active your thyroid is right now. By measuring TSH alongside your free thyroid hormones, you get a picture of the interplay between your brain and your thyroid.

This test can be useful if you recognise symptoms that are sometimes associated with the thyroid. Think of ongoing tiredness, changes in your weight, feeling cold or warm easily, hair loss, dry skin or mood swings.

It can also be helpful if you are simply curious about how your thyroid is doing. You do not need a referral from your GP, so you decide whether and when to take the test.

This thyroid function test measures three values in your blood:

• TSH (Thyroid Stimulating Hormone): the signal from your pituitary gland that tells your thyroid what to do. TSH responds sensitively to change and often gives the first impression of your thyroid function.
• Free T4 (Thyroxine): the free, readily available form of the storage hormone T4. This value shows how much thyroid hormone is directly available to your body.
• Free T3 (Triiodothyronine): the free form of the most active thyroid hormone, which has the strongest effect inside your cells.

Together these three values give a more nuanced view than a single measurement, because you see both the driving signal and the hormones themselves.

The combination of your values can give an impression of the direction your thyroid is working in. A raised TSH with a lower free T4 sometimes fits with a slower thyroid, while a low TSH with higher thyroid hormones can point to a more active thyroid.

Good to know: this test can offer insight, but on its own it does not make a diagnosis. The result is a snapshot that means the most in combination with your symptoms and a doctor's judgement.

This test requires a small blood draw at a certified lab. In the Netherlands you can choose from more than 750 sample locations spread across the country.

After ordering, you pick a location near you and schedule a moment that suits you. The draw itself usually takes only a few minutes, and no referral is needed.

A thyroid blood test can be valuable at different moments, for example:

• when you have symptoms you cannot quite place, such as fatigue or weight changes
• when you previously had off-range thyroid values and want to see how they compare now
• around a wish to conceive, since your thyroid can play a role there
• when you simply want to know how your thyroid is doing

A TSH blood test is often used as a first step, after which free T4 and free T3 help fill in the picture.

Your result shows each value next to a reference range and a short explanation. What counts as usual can vary slightly by laboratory.

A value below or above the range does not automatically mean something is wrong, but it can be a reason for a conversation. The doctor helps you place your values in the right context, so you understand what they may mean for you.

For this thyroid test you usually do not need to fast. Many people have their blood drawn in the morning, because levels can shift slightly during the day, which keeps your measurements more comparable over time.

If you take supplements containing biotin, this can sometimes affect the measurement. If you are unsure, you can check with your GP or the lab.

Your result is usually available online within a few working days. Each value is shown clearly with a reference range and an explanation, so you understand what you see.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.