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Análisis Médicos

Thyroid blood test

A thyroid blood test can look at how the gland is working and what may be causing an abnormality. TSH and the thyroid hormones answer the first question. Thyroid antibodies help investigate the second.

At Análisis Médicos we have designed different profiles for a first assessment, for monitoring hypothyroidism that has already been diagnosed, for investigating hyperthyroidism, and for situations where it makes sense to add micronutrients. The difference is not only how many tests each one includes, but the question it sets out to answer.

Thyroid blood tests available

If you are not sure which one suits you, there is a guide below the list to help you choose.

How it works

You can order any of our thyroid blood tests without your doctor having to request it:

Price
From €35.00
Prescription
Not needed
Appointment
Not needed
Results
1 to 7 working days
  • Your test request, in minutes. Order the profile you want and it arrives in your inbox straight away, with the preparation instructions.
  • Wherever suits you, with no appointment. You can have your test at any of the 45 partner centres, and the laboratory emails you the results within a few days.
  • With an invoice. When you order, you receive an invoice you can submit if you have reimbursement health insurance. How it works, step by step.

How to choose your thyroid blood test

This is not medical advice and does not replace a consultation: it is the reasoning I would use to choose, in case it helps you decide which one to order.

For a first general assessment, the full thyroid blood test brings together TSH, free T4, free T3 and anti-TPO antibodies. It assesses thyroid function and adds the antibody most often requested when an autoimmune cause is being investigated.

To monitor hypothyroidism that has already been diagnosed, the hypothyroidism monitoring blood test focuses on TSH and free T4. It is a deliberately short protocol: it does not repeat tests that do not usually add anything to routine follow-up.

When the assessment is already aimed at possible hyperthyroidism, the hyperthyroidism blood test adds TSI antibodies, which are linked to Graves' disease. It is not designed as a general first-line test.

If you also want micronutrients assessed, the thyroid blood test with key micronutrients extends the profile with iron, vitamin B12, zinc and selenium. The blood test with reverse T3 and micronutrients also adds reverse T3, a secondary test that is not part of the usual assessment of hypothyroidism.

Dr. Antonio Mas

Thyroid function and its cause are not the same question

TSH is the signal the pituitary gland uses to regulate the thyroid. Free T4 is the main hormone the gland produces, and free T3 is a more active hormone that adds information mainly in some assessments of hyperthyroidism. These tests describe thyroid function, but they do not always explain why it is abnormal.

Anti-TPO antibodies are often associated with Hashimoto's thyroiditis. TSI are used in the assessment of Graves' disease. They are different questions, which is why not every profile includes the same antibodies.

Why there is no single thyroid blood test

Monitoring a treatment does not call for the same tests as a first assessment. Investigating possible Graves' disease is not the same as extending a profile with micronutrients either. Adding tests without a specific question can make a blood test more expensive without making it more useful.

Nor do antibodies replace thyroid hormones. They can add information about an autoimmune cause, while TSH and free T4 show how the gland is working at that moment.

What a blood test cannot decide on its own

A blood test does not automatically indicate whether a treatment should be started or changed. Nor does it replace an ultrasound when the question is structural, for example with a nodule or an enlarged thyroid. Those decisions require bringing together medical history, examination, medication and how things evolve over time.

Before your blood test

No fasting is required for these thyroid profiles. If you order them together with another blood test that does require fasting, follow the stricter preparation.

If you take levothyroxine, the sample is usually taken before that day's dose, unless the professional who follows you has told you otherwise.

If you take biotin, check the preparation on the profile page and mention it before the sample is taken. It can interfere with some hormone measurements. Do not stop any prescribed treatment on your own.

To compare successive checks, it helps to have the samples taken under similar conditions of time of day and medication.

Frequently asked questions

Does my GP have to request it?
No. When you order the profile you receive the test request by email and can take it to a partner centre.
Do I have to fast for a thyroid blood test?
Not for the thyroid profiles on their own. If you combine them with another blood test that requires fasting, follow the preparation for that other test.
What is the difference between a thyroid blood test and a thyroid function test?
They are two common ways of referring to a set of thyroid tests. What matters is checking which tests each profile includes, because the content is not always the same.
Which profiles include thyroid antibodies?
The full thyroid blood test includes anti-TPO. The profile aimed at hyperthyroidism adds TSI. The broader profiles can include other antibodies.
Is the most comprehensive blood test always the best?
No. The right test depends on the question. For known hypothyroidism, TSH and free T4 may be enough, while a first assessment or a specific suspicion may call for other tests.

If you already have your results

A figure only makes sense in its context. Medical history, symptoms, medication and the conditions of the sample can change what it means. Results are assessed in a consultation; this page is for comparing and ordering profiles.

The laboratory sends you the results directly. You can then review them with the professional of your choice.

If you already have results, they should be assessed in their clinical context and not by automatically choosing another profile.

See thyroid blood tests

Guide reviewed by Dr. Antonio Mas, specialist in Endocrinology and Nutrition, Spanish medical licence no. 080846289, in September 2026.

And if you were looking for something else, here are all the blood tests in the catalogue, grouped by topic.