Thyroid tests: which ones and how to read them

One blood draw is enough to check your thyroid. It almost always starts with TSH. If needed, your doctor adds FT4, FT3 and antibodies. Here is what each test measures, when it is done and how to read the results together.

What your thyroid does

Your thyroid is a small gland at the base of your neck. Its hormones set how fast your body works: heartbeat, temperature, energy, weight.

It is steered by your pituitary gland, at the base of your brain, with a hormone called TSH. It works like a seesaw: when your thyroid works too little, TSH rises. When it works too hard, TSH falls.

Blood tests measure this signal, the thyroid hormones and, when needed, the antibodies that can attack your thyroid.

Which blood tests check your thyroid

There are six. You do not need all of them, and not all at once:

On your report FT4 and FT3 may also appear as fT4 and fT3, or as free thyroxine and free triiodothyronine.

Why it starts with TSH

TSH moves before the thyroid hormones do. That is why it is the first test for your thyroid, and it often spots a problem before any symptoms.

For people who feel well, TSH is often enough. If it is normal, your thyroid is usually working as it should and the other tests add little.

If it is outside the limits, your doctor asks for FT4 and, depending on the case, FT3 or antibodies.

Many thyroid packages run every test at once. For a first check, in someone who feels well, that is usually not needed.

How to read TSH and FT4 together

Your doctor almost always reads TSH together with FT4. Here are the most common combinations:

High, low and normal mean compared with the limits printed on your report. The table helps you understand, but your doctor makes the diagnosis.
ResultWhat it usually meansWhat happens next
High TSH, low FT4Your thyroid is working too little: this is hypothyroidism.Your doctor looks for the cause, often with anti-TPO antibodies, and decides on treatment.
High TSH, normal FT4Your thyroid is struggling a little but still coping: this is called subclinical hypothyroidism.TSH and FT4 are usually repeated after two or three months, with anti-TPO antibodies. Often no treatment is needed.
Low TSH, high FT4Your thyroid is working too hard: this is hyperthyroidism.Your doctor may ask for FT3 and TRAb to find the cause.
Low TSH, normal FT4Your thyroid may be working a little too hard. Sometimes a thyroid hormone dose that is a little high, early pregnancy or biotin is behind it.Your doctor usually asks for FT3 and checks TSH again before deciding.
Normal TSH, high FT4Often it is not the thyroid: the tablet taken shortly before the draw, some medicines, biotin or the test method.It is usually repeated, sometimes with another method.
Normal or low TSH, low FT4Sometimes an ongoing illness or some medicines are behind it. More rarely the pituitary does not send your thyroid enough signal.Your doctor may refer you to an endocrinologist.
Normal TSH and FT4Your thyroid is usually working well.If tiredness or weight gain will not shift, the cause is usually something else: talk to your doctor.

Symptoms: when to think of your thyroid

Thyroid problems are common, especially in women, and they often come on slowly. Sometimes there are no symptoms. When there are:

These symptoms are common and have many other causes. TSH helps show whether your thyroid is involved. If you have them, talk to your doctor.

Calcitonin and thyroglobulin are not check-up tests

They appear in some thyroid packages, but they do not check the thyroid in people who feel well. A specialist asks for them in specific cases:

In someone with no reason to have them, a slightly high result often brings only doubts. It almost always has causes other than cancer.

What can skew the results

Some things change the values without a thyroid problem. It helps to know them before the draw:

Your thyroid in the Rosa panel

Rosa measures TSH once a year, in the first draw. It is the first test for your thyroid, and in your report you find it explained together with the rest of the panel.

FT4, FT3 and thyroid antibodies are not in the Rosa panel. If your TSH is outside the limits, talk to your GP, who can order them.

A licensed physician approves every report before you see it.

When to see a doctor

Talk to your doctor if:

Blood tests show how your thyroid is working, not always why. Your doctor finds the cause, sometimes with an ultrasound.

Other guides

Frequently asked questions

Which blood tests check the thyroid? TSH comes first. Then, when needed, FT4 and FT3, the thyroid hormones, and the antibodies: anti-TPO, anti-thyroglobulin and TRAb. Calcitonin and thyroglobulin are only for specific cases.

Do I need all the thyroid tests at once? Usually not. For a first check in someone who feels well, you start with TSH. If it is outside the limits, your doctor adds FT4 and, if needed, the others.

Do I need to fast for thyroid tests? It depends on the lab: ask when you book. They are often done with other tests, like glucose and triglycerides, that do need fasting. To compare two tests, have them under the same conditions.

Should I take my thyroid tablet before the draw? Ask your doctor. In the hours after the tablet FT4 rises a little, so you are sometimes told to take it after the draw, on the day of the test. Do not change or skip the dose on your own.

How often should my thyroid be checked? For people who feel well there is no fixed rule. In the Rosa panel TSH is measured once a year. If it is slightly high, your doctor usually repeats it after two or three months, together with FT4. If you take a thyroid medicine, follow your doctor’s timing.

Do blood tests show thyroid nodules? No. With a nodule TSH is often normal. Nodules show up on a neck ultrasound, which is not a blood test. If you feel a swelling at the base of your neck, talk to your doctor.

Does Rosa test FT4, FT3 and antibodies? No. Rosa measures TSH, the first thyroid test, once a year. If your doctor wants FT4, FT3 or antibodies, they order them separately.

Keep an eye on your thyroid

TSH is one of the 31 tests in the first Rosa draw, alongside those for your heart, blood sugar, liver, kidneys, blood, iron and vitamins. Every value explained and a doctor who approves your report. At a partner lab, no prescription needed. €295 a year.

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