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Advanced Thyroid Function Blood Test, from our experts to you.
Dr Sam Rodgers MBBS, MRCGP

Chief Medical Officer

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What is the
Advanced Thyroid Function Blood Test?

Our Advanced Thyroid Function Blood Test is our most comprehensive thyroid test and contains everything you need to give you a clear picture of your thyroid health. It tests how well your thyroid is functioning and whether an autoimmune disorder could be causing your symptoms.

What can I learn
from this test?

This test helps you understand whether any symptoms you are experiencing could be caused by an overactive or underactive thyroid. It includes 3 important thyroid-related hormones to help explain any symptoms you may have. These include free thyroxine (FT4) and the more biologically active free triiodothyronine (FT3) as well as thyroid stimulating hormone (TSH). The majority of thyroid disorders are caused by autoimmune conditions where your body's immune system attacks the thyroid gland. This test measures your thyroid antibodies (thyroglobulin and thyroid peroxidase antibodies) to help you learn whether an autoimmune condition could be affecting your thyroid function.

Why check for
vitamins and minerals?

Our advanced profile includes relevant vitamins and minerals which support your thyroid function and can mimic the symptoms of an underactive thyroid if they are low. We have included tests for vitamin D, vitamin B12, folate (vitamin B9), and ferritin (a marker for iron storage). We also test an inflammation marker to help interpret your iron (ferritin) result and to give a picture of whether an autoimmune condition is causing inflammation in your body.

What's Included?

Iron status
Thyroid hormones
Select profile for more information

Thyroglobulin antibodies This test looks for antibodies to thyroglobulin, a protein which is specific to the thyroid gland. Under normal circumstances it does not enter the bloodstream, but if your thyroid is inflamed or under attack from the body's own immune system, then thyroglobulin can be secreted and antibodies detected. Most cases of thyroid disease are caused by an autoimmune condition where the thyroid gland is attacked by the body's own immune system. This can cause the thyroid gland to produce more thyroid hormone (as in the case of Graves' disease) or to produce less as the cells in the thyroid gland are gradually destroyed (as in the case of Hashimoto's thyroiditis).
Thyroid peroxidase antibodies Thyroid peroxidase (TPO) is an enzyme important in the production of thyroid hormones. This test looks for antibodies against TPO which are often raised in cases of autoimmune thyroid conditions and occasionally in healthy individuals.
hs - CRP C-Reactive Protein (CRP) is an inflammation marker used to assess whether there is inflammation in the body - it does not identify where the inflammation is located. High Sensitivity CRP (CRP-hs) is a test used to detect low-level inflammation thought to damage blood vessels which can lead to a heart attack or stroke. When you suffer a serious injury or infection you experience significant inflammation around the site of injury - such as the swelling around a twisted ankle. Any injury like this will cause your CRP-hs to rise.
Ferritin Ferritin is a protein which stores iron in your cells and tissues. Usually, the body incorporates iron into haemoglobin to be transported around the body, but when it has a surplus, it stores the remaining iron in ferritin for later use. Measuring ferritin levels gives us a good indication of the amount of iron stored in your body.
TSH Thyroid stimulating hormone (TSH) is produced in the pituitary gland in order to regulate the production of thyroid hormones thyroxine (T4) and triiodothyronine (T3) by the thyroid gland. If thyroid hormones in the blood are low, then more TSH is produced to stimulate the thyroid gland to produce more of them. If thyroid hormone levels are high, then the pituitary produces less TSH to slow the production of thyroid hormones. If TSH is too high or too low, it normally signifies that there is a problem with the thyroid gland which is causing it to under or over produce thyroid hormones. Sometimes a disorder of the pituitary gland can also cause abnormal TSH levels.
Free T3 Triiodothyronine (T3) is the more active of the two thyroid hormones produced by the thyroid gland. Most T3 is bound to protein in the blood. Free T3 measures the level of T3 that is free, or unbound to protein, and is available to regulate metabolism.
Free thyroxine Thyroxine (T4) is one of two hormones produced by the thyroid gland. It works to speed up the rate of your metabolism. Most T4 is bound to carrier proteins in the blood - it is only the free, or unbound, T4 that is active in the body, which is measured in this test. Free T4 is the less active of the two main thyroid hormones. To have an impact on your cells it needs to convert to the more active T3 when your body needs it.
Folate - serum Folate is a B vitamin which acts as a coenzyme in the metabolism of amino acids. It is also vital for the synthesis of purines and pyrimidines which are essential for DNA synthesis and red cell formation. Folate is also especially important during the first trimester of pregnancy so if you are thinking of becoming pregnant it is important to make sure your folate levels are normal.
Vitamin B12 - active Vitamin B12 is important for production of red blood cells which carry oxygen around the body. B12 is also involved in metabolism and the nervous system and prolonged lack of vitamin B12 may cause nerve damage. Although Vitamin B12 is almost entirely found in animal-based foods, many vegetarian and vegan products, especially plant milks are now fortified with Vitamin B12.
Vitamin D Although called a vitamin, vitamin D is actually a hormone which is activated by sunshine on your skin. Vitamin D is essential for bone strength as it helps your intestines absorb calcium. However, it is thought that vitamin D also plays an important role in immune function, as well as in many chronic diseases and mental health. Many people in the UK have low levels of vitamin D with symptoms including muscle weakness, mood swings and fatigue. People who have dark skin, as well as those who don't spend much time outdoors are particularly at risk of low vitamin D. Small amounts of vitamin D can be obtained from food, especially oily fish, eggs and any food which has been fortified with vitamin D. If you are deficient in vitamin D you are unlikely to be able to improve your levels by food alone.

How to prepare
for your test

Special Instructions

Prepare for your Advanced Thyroid Function Blood Test by following these instructions. Please take your sample before 10am. Take this test when any symptoms of short-term illness have settled. You should take this test before you take any medication or vitamin/mineral supplements. Do not take biotin supplements for two days before this test, discuss this with your doctor if it is prescribed. Do not take vitamin B12 for two weeks prior to this test. If your B12 is prescribed ask your doctor whether to stop.

Frequently asked questions

How do you test your thyroid?

If you are experiencing thyroid-related symptoms, such as changes with your weight, energy, mood, skin or hair, then a thyroid blood test will help you to test your thyroid function. We have three popular thyroid tests to help you understand whether you have the right level of thyroid hormones for a healthy metabolism.

What is the best blood test for thyroid?

Private thyroid tests can give you access to the full range of thyroid hormones, thyroid antibodies and nutrients that can affect your thyroid health, together with the added advantage of a convenient and speedy service. The blood tests available from your GP often only routinely test your thyroid stimulating hormone (TSH) and free thyroxine (FT4).

Look at the different types of thyroid blood tests with our Thyroid Buying Guide.

Does fasting affect thyroid blood test?

In general, you do not need to fast before a thyroid blood test. If you are required to fast, you will be told in advance. It is best to fast overnight and take your test in the morning so that you don’t have to go too long without eating.

It is, however, very important to make sure that you are well-hydrated before taking a blood test. Read our top tips for taking a finger-prick blood test or look at our Frequently Asked Questions for more information.

How do you test for underactive thyroid?

The best way to test for an underactive thyroid is through a thyroid blood test. However, it isn’t always enough to just focus on thyroid function. Symptoms which may be associated with an underactive thyroid could also be caused by other conditions such as iron deficiency anaemia, a nutritional deficiency or a hormone imbalance.

To diagnose an underactive thyroid, your doctor will look at your symptoms together with the results of blood tests that measure the level of your thyroid hormones.