The thyroid gland, located in the neck and shaped like a butterfly, has one of the most important functions in the body, without detracting from the other components. Its task is to control nothing less than general metabolism through the production of thyroid hormones, in particular thyroxine and triiodothyronine. The fact that it has such an indispensable function in the body means that, if there is a problem or irregularity in its production, the consequences can be very serious. Hence, if there is any suspicion, a complete thyroid analysis or thyroid profile should be performed. These tests can help us to detect problems early and find solutions. Let us look at what the analysis consists of and how the results are interpreted.
What does a complete thyroid analysis consist of?
As we have briefly explained, the thyroid profile consists of a series of tests that measure the functioning of the thyroid gland to detect possible thyroid diseases. These hormones are responsible for telling cells throughout our bodies how fast to use their energy and how to synthesise proteins. One of the hormones in this group is calcitonin, which regulates calcium levels in the blood by inhibiting bone reabsorption and increasing calcium excretion through the kidneys.
However, the most commonly produced thyroid hormones are thyroxine (T4) and triiodothyronine (T3). To control the amount of TSH in the blood, our body relies on a feedback system consisting of TSH, synthesised by the pituitary gland, together with the hormone that regulates it (TRH), produced in the hypothalamus.
In a healthy, normally functioning body, this feedback system works perfectly and keeps thyroid hormone concentrations in the blood ‘in check’. A complete thyroid work-up usually includes the following tests:
- TSH (thyrotropin).
- Free T4(thyroxine).
- Free T3(triiodothyronine).
- Total T4(thyroxine).
- Total T3(triiodothyronine).
Most of the triiodothyronine and thyroxine in the blood moves bound to certain proteins. Those that do not, called ‘free’, are the biologically active hormones. It is necessary to measure the 2 types separately and then analyse the results together.
It should be noted that the results of the total T3 and T4 fractions can be affected by the amount of protein in the blood available to bind to them. In fact, the ‘free’ hormones are more reliable, so to speak, as they more accurately reflect the function of the thyroid gland.
Years ago, a complete thyroid work-up used to be performed much more frequently, but nowadays the procedure has changed: a screening test is now ordered first and additional tests are added to reduce the number of tests a patient would have to undergo. It should be borne in mind that it is a long and tedious process for the patient, so any reduction in time is always welcome.
TSH is usually the first test performed and, depending on the results obtained, together with the signs and symptoms present, other tests are added. It should always be borne in mind that thyroid hormone concentrations can be affected by:
- Variations in the concentrations of T4- and T3-binding proteins.
- Pregnancy.
- Oestrogens and other drugs.
- Liver diseases.
- Systemic diseases.
- Resistance to thyroid hormones.
In fact, there are some medications that can alter thyroid hormones: most multivitamins and supplements (especially hair and nail supplements) can affect the test. If the patient is taking any such medication, it is essential that they tell their doctor so that he or she can determine the next step to consider.
There is also a battery of tests that we detail below to rule out an autoimmune origin when a thyroid problem appears:
- Anti Microsomal Antibodies (TPO fraction)
- Anti-thyroglobulin antibodies
- Anti TSH receptor antibodies
- Anti-T4 antibodies.
How does the feedback system work?
If the blood concentration of thyroid hormones drops, the body has a system that ‘alerts’ the hypothalamus to release thyrotropin, a regulatory hormone that causes the pituitary gland to produce thyroid stimulating hormone (TSH). This gives the thyroid a ‘wake-up call’ to start producing more T3 and T4. As the amounts of both hormones increase, the other factors that have helped to promote their production ‘switch off’: the pituitary gland produces less TSH and, in turn, the thyroid produces less T4 and T3.
Problems arise when this system does not work because the thyroid is not able to produce enough T4 and T3 even though the pituitary gland is prompting it to do so. This is where some symptoms of hypothyroidism may arise (to be explained later).
If the opposite happens and the thyroid produces too much T4 and T3, this is not a good thing either, as we can find ourselves with a surplus of these hormones, which can lead to hyperthyroidism. Both can also be caused by thyroiditis, thyroid cancer and excessive or deficient TSH production.
When is it requested?
Your health care professional may order a complete thyroid panel if certain symptoms of hypothyroidism or hyperthyroidism, caused by thyroid disease, are observed. Some of them in the case of hypothyroidism are:
- Decreased heart rate.
- Weight gain.
- Enlargement of the thyroid (goitre).
- Dry skin.
- Constipation.
- Intolerance to cold.
- Muscle and joint pain.
- Thickening of the skin.
- Hair loss.
- Fatigue.
- Depression.
- Mental gaps.
- Menstrual irregularities.
- Infertility (in women).
On the other hand, the most common signs of hyperthyroidism are:
- Increased heart rate.
- Anxiety.
- Weight loss.
- Difficulty sleeping.
- Trembling hands.
- Muscle weakness.
- Increased sweating.
- Difficulty in coping with heat.
- Diarrhea.
- Swelling around the eyes, dryness, irritation, and sometimes bulging eyes.
- Menstrual irregularities (less frequent or lighter periods).
Tests for the diagnosis of thyroid diseases
Blood tests. A blood test can provide invaluable information about the thyroid by measuring levels of thyrotropin pituitary hormone (TSH) and active thyroid hormones in the blood. It is best to find out the free portion of thyroxine and triiodothyronine because there are certain occasions (pregnancy or contraceptive use) when the protein level in the blood is altered without altering thyroid function.
Cervical ultrasound. This technique uses ultrasound to diagnose thyroid diseases by imaging, and is one of the most loved by patients because it is painless, does not require the interruption of any medication, has no irradiation, and provides doctors with excellent information about the thyroid gland image.
Thyroid scan. This test requires avoidance of excess iodine 1 week before the test, but is able to see the functionality of the thyroid, whether it is inflamed and whether it is functioning homogeneously or heterogeneously (whether one part works more than the other). It is very useful in possible cases of hyperthyroidism, but is of little use if hypothyroidism is suspected.
Ultrasound-guided fine needle aspiration-fine needle aspiration (FNA). A thyroid puncture is performed (2 to 3 punctures are often needed for each procedure), obtaining a cytological sample of thyroid cells to determine whether they are malignant or benign. Although it does not usually leave sequelae, it is advisable not to do physical exercise that involves significant contraction of the cervical musculature on the day of the test.
Magnetic resonance imaging. It is particularly practical when there is a possibility that the patient may have thyroid cancer, as this test allows the infiltration of local structures to be assessed thanks to its resolution, which is superior to that of CT images.
What do the results mean?
If the feedback system related to the thyroid gland is not working properly, this can lead to a rise or fall in the amount of thyroid hormones, as mentioned above. The results of a complete thyroid scan are not a diagnosis by themselves, but can help the doctor to guide him or her on the right path. In any case, additional tests will always be performed to ascertain the cause of this excess or deficiency and the thyroid disease causing it.
An adult is considered to have subclinical hypothyroidism when the TSH concentration is high and free T4 is normal, with repeat testing over several weeks or months. The main problem with hypothyroidism in adults is that the symptoms of the disease are often very mild or even absent. Even so, suffering from it generates an increased risk of elevated LDL-cholesterol values, cardiovascular disease and/or reduced mental acuity.
On the other hand, an adult with subclinical hyperthyroidism will be considered as such when a low TSH concentration and normal free T4 and T3 concentrations are observed, again based on repeated testing over several weeks or months. As no strong symptoms are usually noticeable either, it is still essential to locate the source of the problem as quickly as possible, as hyperthyroidism can lead to an increased risk of atrial fibrillation and osteoporosis.
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