Thyroid Function Test BASIC

What’s measured

Why undergo a Thyroid Function Test BASIC?

This test package is suitable for individuals interested in assessing the function of their thyroid gland.

The thyroid gland, an endocrine organ, synthesises the hormones thyroxine (T4) and triiodothyronine (T3). Dysfunctions of this gland can present as local changes in the neck area (goiter), but more prominently as systemic metabolic manifestations due to inadequate or excessive hormone production. Thyroid activity is regulated by hormones secreted by the pituitary gland, including thyrotropin-releasing hormone (TRH) and thyroid-stimulating hormone (TSH)

Symptoms of thyroid disorders are indicative of either inadequate or excessive hormone production. These symptoms encompass fatigue, hair loss, changes in weight, heart palpitations, tremors in the limbs, swelling, hot flashes or chills, and dry skin, among others [1].

Thyroid Function Test BASIC includes

TSH – thyrotropin, thyroid-stimulating hormone

TSH is a hormone produced by the cells of the anterior lobe of the hypophysis/pituitary gland. It affects the metabolism of thyroid cells and stimulates the production and secretion of thyroid hormones, especially thyroxine (T4) and triiodothyronine (T3).

fT3 – free triiodothyronine

Free T3 (fT3) is an active form of triiodothyronine (T3) – a hormone produced primarily in the thyroid gland. The effect of the free fraction of the T3 hormone is approximately 10-times higher than that of thyroxine. Many serious health conditions, such as cancer or a critical threat to life, may be accompanied with the low T3 syndrome; in such as case, the physiological levels of TSH and fT4 are tested at a decreased level of T3 (total and free).

ft4 – free thyroxine

Free T4 (fT4) is a physiologically active form of thyroxine. Thyroxine (T4) is one of the two main thyroid hormones. It is produced exclusively in the thyroid gland and it is a natural part of the thyroid gland regulatory system. It also affects the overall metabolism. Moreover, it is a prohormone of the biologically more active triiodothyronine (T3).

Instructions before collection

We do not recommend entry of patients/clients with clinical signs of disease (temperature, cough, signs of respiratory tract infection, etc.) to undergo this test.
We recommend hand disinfection prior to entry to the clinics/collection points.

It is advised to fast for a minimum of 8 hours by refraining from eating or drinking anything expect water. Faiing to fast before the test may affect result quality. If you are currently on medications, consult your healtcare provider to determine whether you should continue taking them prior to the test.

PREPARATION FOR BLOOD COLLECTION
The recommended time to collect blood is between 7 a.m. and 9 a.m., to obtain comparable results from different blood draws. To assess the numerical test result, so-called reference intervals are used, which are based on morning fasting collections and are used for population comparison. This time interval is also recommended in light of the biological cycles that naturally take place in the body.

GENERAL PRE-SAMPLING INSTRUCTIONS
• It is necessary to come to the testing site earlier, so that you can rest in the waiting room for approximately 20 minutes to have a relatively relaxed body and mind.
• It is not advisable to draw blood before collection.
• It is necessary to arrive on an empty stomach for the collection itself, in the case of collections at a later time in the day, at least three hours on an empty stomach. At home, it is desirable to drink a sufficient amount of pure water (at least up to half a liter) - this is important for a successful blood collection. Mineral water, juice, coffee and tea are not recommended.
Herbs included in tea may contain substances affecting the blood count. Coffee and black tea increase gastric acid production and release insulin from the pancreas, thereby affecting glucose metabolism. Since everything in the body is interrelated, they can impact other tests. Another extreme is when your body is running out of fluids. In this case, the number of red blood cells, the level of protein and lipids bound to the protein increase and the level of urea in the blood can also increase. It is therefore advisable to drink pure water when you wake up.


Generally, it is recommended to:
• around 6 p.m. eat only light meals, do not eat fatty food (cheese, butter, cream, meat, smoked meat, bacon) and sweet meals,
• fast for 10-12 hours (Attention: it is not advisable to starve for more than 16 hours!), in the case of later collection (after 9:30 a.m.), a lighter breakfast is allowed, no later than 3 hours before collection,
• drink non-alcoholic beverages and drinks without sugar in the usual quantity, in the case of adult clients 24 hours before blood collection (Alcohol in the blood changes lipid levels, the level of glucose is reduced, uric acid levels increase and liver enzymes are released into the blood),
• take only prescribed medicines in the evening,
• avoid increased physical activity, and strength and endurance exercise the day before blood collection (Lipid, glucose, some enzyme levels in the blood and other parameters may change during physical activity. The recovery of normal values to maintain the accuracy of laboratory results may take a longer time, depending on the duration of the exercise, your physical fitness in general and other factors. We recommend maintaining normal daily physical activity such as light stretching, short cycling to work, gardening, etc.),
• avoid psychological stress, which raises blood glucose levels and causes the release of stress hormones in particular,
• avoid smoking for at least 6 hours prior to blood collection because it increases the level of carbonylhemoglobin produced by the reaction of the blood dye with carbon monoxide and alters the permeability and elasticity of the vessels, affecting the ratios of blood analytes,
• do not chew gum for at least 6 hours before blood collection, as this may affect glucose and enzyme levels,
• do not undergo stressful diagnostic or therapeutic interventions for at least 24 hours prior to blood collection.
If any of the tests you have selected require special preparation, you will be informed of the fact by email with the order and blood collection instructions attached. These specific instructions have priority over the general recommendations for preparation.


MEDICINES
It is recommended to have blood collected before the planned doses of medicines. If it is not possible to take the medicine later, you should inform the nurse during blood collection and specify what medication you have taken.
Take the medicines prescribed by your doctor in the morning or bring them with you to take them after blood collection (thyroid medicines, antihypertensive medicines, blood thinners, contraceptives, etc.) In the case of later collection (after 9:30 a.m.), you can take the prescribed medication in the morning.
Do not take iron, vitamin, nutritional supplements or other supplements, including homeopathics, for at least three (3) days prior to blood collection.


SPECIFIC SITUATIONS
In order to obtain the appropriate answers to your questions with regard to the laboratory tests, it is important to accurately notify the nurse at the healthcare provider about the following facts prior to your blood test:
• regularly used medicines and supplements (ideally come with a written list to the blood collection site),
• infectious diseases you suffer from (e.g., HIV, hepatitis, mononucleosis...),
• contact with an infected person or presence in an infectious environment,
• if you have received an infusion within the last 5 days, specify into which limb,
• intramuscular injections within 3 days prior to the blood collection date,
• long-term immobilisation, lost ability to move,
• activities at higher altitudes,
• allergy to common band-aids,
• if you feel unwell when looking at blood or needles, please also notify our blood collection staff of the fact.


OTHER FACTORS
Please note that prolonged use of medication or other important factors may affect the values measured by the tests you have selected. For more information, please see the description of the specific test. To obtain objective test results, take the time to properly prepare for your blood collection.

Sources

[1]Ďuriš I., Hulín I., Bernadič M. et al. Princípy internej medicíny. SAP, p. 2011-2044