Thyroid blood test with key micronutrients

Secondary relevance

Thyroid blood test with hormones, antibodies and a selection of micronutrients that matter for the thyroid: selenium, zinc, ferritin, vitamin B12 and vitamin D. It is designed to assess thyroid function and, at the same time, check for a nutritional deficiency that could cause similar symptoms or add context to a known thyroid condition.

No prescription or appointment needed

Results in 3-5 working days

Includes: TSH · Free T4 · Free T3 · Thyroid peroxidase antibodies · Thyroglobulin antibodies · Selenium · Ferritin · Zinc · Vitamin B12 · Vitamin D. See what each one measures

Secondary relevance. It is not the one I recommend to start with. It is here because it adds something in specific situations, but for most people it looks at more than is needed.

What it is for

This profile extends the standard thyroid assessment in two directions. On one hand, it looks at thyroid function and the two antibodies most used to investigate possible autoimmune thyroiditis. On the other, it measures several micronutrients linked to thyroid metabolism or to symptoms that can be mistaken for those of hypothyroidism.

It can make sense with known autoimmune thyroiditis, with persistent symptoms that thyroid function alone does not explain, or with restrictive diets when nutritional status also needs assessing.

It is not the usual first assessment for everyone. For a first look, the full thyroid blood test is usually enough, and for monitoring hypothyroidism that is already being treated, the TSH and free T4 blood test is usually sufficient. This profile is designed for people who also want an answer to a nutritional question.

When it is recommended

Diagnosed Hashimoto's thyroiditis, at a review
Persistent symptoms with apparently normal thyroid function
Tiredness and hair loss with inconclusive previous blood tests
Long-term restrictive diets together with thyroid disease
When you want to extend the thyroid and nutritional assessment in a single sample

Clinical comment

The micronutrients in this profile do not all carry the same clinical meaning. It is worth separating their biological role from the usefulness of measuring them routinely.

Selenium and zinc are involved in thyroid hormone metabolism. Bear in mind that this biological link does not mean that measuring them is indicated in everyone with thyroid symptoms.

Ferritin answers a more practical question: iron deficiency can cause tiredness, hair loss and lower exercise tolerance. Measuring iron stores helps avoid automatically blaming those symptoms on the thyroid.

Vitamin B12 is not included because it regulates thyroid function, but because of the link between different autoimmune conditions. Vitamin D is part of the general nutritional assessment; measuring it does not mean that a supplement will treat thyroiditis or correct thyroid function.

The antibody block is wider than in the first-line profile because it adds thyroglobulin antibodies. They perform less well than anti-TPO, but they can add information in some cases of suspected autoimmune thyroiditis with negative anti-TPO.

Dr. Antonio Mas

What is tested

TSH: The hormone the pituitary gland uses to regulate the thyroid. It is usually the first test to change and guides the rest of the investigation.
Free T4: The main hormone produced by the thyroid, measured in its free fraction. It shows how much thyroxine is available in the blood.
Free T3: The thyroid hormone with the greatest activity in the tissues. It is particularly useful when TSH is low and possible hyperthyroidism is being investigated.
Thyroid peroxidase antibodies (anti-TPO): Antibodies against thyroid peroxidase. Their presence supports an autoimmune origin, such as Hashimoto's thyroiditis, although they can also appear in people with normal thyroid function.
Thyroglobulin antibodies (anti-Tg): They look for further signs of thyroid autoimmunity and can add information when anti-TPO is negative.
Selenium: Involved in the enzymes that convert T4 into T3 and in the thyroid's antioxidant systems.
Ferritin: Reflects iron stores. Iron deficiency can cause tiredness, hair loss and other symptoms that are also attributed to hypothyroidism.
Zinc: Involved in the metabolism and action of thyroid hormones.
Vitamin B12: Included because some autoimmune conditions linked to its deficiency are more common in people with autoimmune thyroiditis.
Vitamin D (25-OH): Assesses vitamin D status as part of the general nutritional assessment, not as a thyroid treatment.

How to prepare

No fasting is required for the thyroid tests. If you take biotin supplements (vitamin B7, common in hair and nail complexes), stop them 48 hours before: they interfere with the measurement of several thyroid hormones and can give falsely abnormal results. If you take levothyroxine, the sample is taken before that day's dose.

You can add

Without another needle. It is offered when you order, so you do not have to decide now.

General blood testA general blood test with full blood count, glucose, cholesterol and kidney and liver function: the basic parameters included in any general check-up.+€59.00
Coeliac disease antibodiesMeasures the antibodies used to investigate coeliac disease; for a reliable result, it must be done while you are still eating gluten.+€39.00

Related blood tests

We have other profiles in Thyroid with more or fewer tests:

The most comprehensive is not always the most useful. If you are not sure, the one we recommend to start with is Full thyroid blood test with anti-TPO antibodies.

What it is based on

The thyroid function and antibody block is based on the reference clinical guidelines. The role of iron, selenium and zinc in the synthesis and metabolism of thyroid hormones is described in the scientific literature. That is not the same as a screening recommendation: the guidelines do not advise measuring these micronutrients routinely in everyone whose thyroid is being assessed. They are included in this protocol when the clinical question also covers nutritional status and possible overlapping symptoms. That is precisely why this profile is marked as secondary relevance.

Zimmermann MB, Köhrle J · Thyroid 12(10):867-878
The Impact of Iron and Selenium Deficiencies on Iodine and Thyroid Metabolism: Biochemistry and Relevance to Public Health
Describes how iron deficiency reduces the activity of thyroid peroxidase, which is a haem enzyme, and how selenium is involved in thyroid hormone metabolism.
Köhrle J · International Journal of Molecular Sciences 24(4):3393
Selenium, Iodine and Iron: Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism
A recent review of the role of selenium in the deiodinases, the enzymes that convert T4 into T3.

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

This blood test is a standardised protocol and does not replace a medical consultation. If you have symptoms, a known condition or a complex clinical situation, speak to your doctor.