What are thyroid function tests (T3, T4, TSH, Anti-TPO)? -Prof. Dr. Muharrem Kıskaç The thyroid gland secretes some hormones that are vital for our body. Some disorders in the secretion of these hormones (thyroid dysfunctions) are very common. In addition, thyroid dysfunctions immediately come to mind in health problems such as rapid weight gain, rapid weight loss, hair loss, fatigue, sweating, palpitations, and tests are requested in this direction. Tests frequently used in the measurement of thyroid functions are the measurement of blood levels of free T3, free T4 and TSH hormones. The best information about the function of the thyroid gland is given by the TSH measurement. The screening test for the thyroid is the TSH measurement. The TSH (Thyroid stimulating hormone) hormone is secreted from the pituitary gland in our brain and shows its effect on the thyroid gland. Changes in the TSH level provide information like a warning system in the early stages of the disease when the T3 and T4 measurements secreted from the thyroid gland have not yet been affected. After the TSH stimulus from the thyroid gland itself, T4 and more T3 hormones are secreted. Since the levels of proteins that bind and carry these hormones in the blood can change due to various diseases or drugs, measuring the total levels of T4 and T3 can be misleading. For this reason, Free T3 (fT3), Free T4 (fT4) levels are used to evaluate thyroid functions. In other words, fT3, fT4 and TSH tests are basically used to evaluate thyroid functions. How do thyroid function tests change in some diseases? Hyperthyroidism: The most sensitive method for diagnosing hyperthyroidism is TSH measurement. High thyroid hormones (Free T3 (fT3), Free T4 (fT4)) together with low TSH suggest hyperthyroidism, that is, rapid thyroid activity and thyrotoxicosis (high thyroid hormone levels, excessive hormone levels outside of rapid activity are also included in this situation). Subclinical Hyperthyroidism: Low serum TSH concentration and normal fT3 and fT4 values ​​suggest the diagnosis of subclinical hyperthyroidism. Hypothyroidism: T3 hormone measurement is not useful in the diagnosis of hypothyroidism. Therefore, its use is not necessary. Hypothyroidism is divided into 2 as primary (more common) originating from the thyroid gland and secondary (secondary) originating from the pituitary gland. If there is primary hypothyroidism, fT4 is low, but TSH is high. In secondary hypothyroidism, fT4 is low, TSH is normal or low. Subclinical Hypothyroidism: Here fT4 is normal, but TSH is high. Thyroid autoantibody tests In cases such as various infections in our body, our immune system cells create antibodies against these microorganisms. In some cases, in autoimmune disease cases, the immune system perceives its own body cells as foreign and creates antibodies against them. These antibodies are called autoantibodies. These autoantibodies are also used in the diagnosis of thyroid diseases, but they are generally not used in follow-up. Anti-TPO (Thyroid peroxidase antibody): Serum anti-TPO measurement is frequently used in the investigation of autoimmune thyroid diseases (AITD). Anti-TPO is valuable in the diagnosis of Hashimoto's thyroiditis, and is also detected in postpartum thyroiditis and Graves' disease. Anti-TG (Anti-thyroglobulin): In most autoimmune thyroid diseases, if anti-TPO is positive, anti-TG is also mostly positive. In a small number of cases, anti-TPO may be negative and anti-TG positive. Therefore, its use is limited compared to anti-TPO. (In the follow-up of thyroid cancer, anti-TG is also checked together with thyroglobulin, and in this respect it is important in this patient group) TSI (Trak, trab) (Thyroid receptor antibody): This antibody supports the diagnosis of Graves' disease. Acute and chronic complications of diabetes • Acute and chronic complications of diabetes... Symptoms of diabetes (diabetes mellitus) and criteria for diabetes diagnosis • Symptoms of diabetes (diabetes mellitus)... What is biotin? What does biotin do? What are the sources of biotin? • What is biotin? What does biotin do? Bi... What is melatonin? What does melatonin do? • What is melatonin? What does melatonin do... What are the benefits of avocado? Avocado ... 8 important benefits of intermittent fasting • 8 important benefits of intermittent fasting What is iron deficiency anemia? What causes it, what are the symptoms • What is iron deficiency anemia? Why... Vitamin D, vitamin D deficiency, vitamin D benefits • Vitamin D, vitamin D deficiency, D ... WHAT IS SELENIUM? IMPORTANCE, BENEFITS AND TREATMENT OF SELENIUM • Selenium, what is Selenium, selenium f... SYMPTOMS, DIAGNOSIS AND TREATMENT OF FATTY LIVER • Fatty liver, fatty liver... SYMPTOMS OF ZINC DEFICIENCY • Zinc, what does zinc deficiency lead to MAGNESIUM (IMPORTANCE AND SYMPTOMS OF DEFICIENCY) • MAGNESIUM (IMPORTANCE AND SYMPTOMS OF DEFICIENCY) • VITAMIN B12 (IMPORTANCE, 10 SYMPTOMS OF DEFICIENCY AND 10 RE