Normal values ​​of three thyroid function tests

As we all know, the thyroid gland is an endocrine organ in the body. Many times, our bodies will develop thyroid diseases due to too much or too little iodine. When doing a thyroid check, doctors generally recommend that you do three thyroid function tests. So, do you know what the three normal values ​​of thyroid function are? Today we will introduce it to you.

Thyroid function test is an endocrine test performed by drawing blood. It can check the basic function of the thyroid gland and determine whether there is hyperthyroidism, hypothyroidism or other abnormalities.

The three thyroid function tests are total triiodothyronine T3, total thyroxine T4, and thyrotropin TSH.

They have the following meanings:

Clinical significance of total triiodothyronine (T3):

(1) Increased TT3: ① TT3 is a more sensitive indicator for diagnosing hyperthyroidism. In hyperthyroidism, TT3 can be 4 times higher than the normal value. ② At the same time, TT3 is a specific indicator for diagnosing T3 type hyperthyroidism.

(2) Decreased TT3: Common in cases of hypothyroidism.

(3) Low T3 syndrome: Although T3 is reduced, there are no symptoms of hypothyroidism. It can be seen in acute and severe diseases such as pernicious anemia, acute myocardial infarction, cirrhosis, uremia, and chronic wasting diseases.

Clinical significance of total thyroxine T4:

(1) Glucocorticoids can reduce the levels of TSH and thyroid binding globulin (TBG) in the blood. Therefore, hypercortisolism caused by various reasons can result in a decrease in serum TT4.

(2) In the early stages of subacute thyroiditis and chronic lymphocytic thyroiditis, due to the destruction of thyroid follicles, the release of thyroid hormones increases, and TT4 often increases. In the later stages, due to excessive destruction of follicles, the synthesis and release of thyroid hormones decrease, and the TT4 level may decrease.

(3) The concentration of thyroid hormone-binding globulin (TBG) in the blood is an important factor affecting TT4 levels. The TT4 concentration was increased in patients with high TBGemia, whereas it was decreased in patients with low TBGemia.

(4) Various drugs can affect TT4 levels through different links, such as iodine-containing drugs, estrogen, contraceptives, beta-blockers, etc. When measuring thyroid hormones, care should be taken to eliminate their interference.

Clinical significance of thyroid stimulating hormone (TSH):

(1) Elevated serum TSH: commonly seen in primary hypothyroidism, TSH-secreting tumors, iodine-deficient endemic goiter, thyroid hormone resistance syndrome, etc.

(2) Decreased serum TSH: commonly seen in primary hyperthyroidism, TSH gene mutation, various pituitary diseases (such as pituitary adenoma, pituitary inflammation, pituitary hemorrhagic disease or traumatic disease, etc.) affecting TSH cell function, the injury phase of various thyroiditis, and the clinical use of high-dose glucocorticoids.

Some people may ask, when should we do three tests and when should we do five tests? Is five tests better than three tests?

In fact, this is not the case. The items for physical examination should be determined according to the specific situation.

If you are doing early screening of thyroid function, it is usually enough to check only three thyroid function tests.

First, the three thyroid function tests can roughly reflect the status of thyroid function; second, thyroid function tests are not cheap, and there is no need to do more expensive tests in the initial screening stage; third, the measurements are easily affected.

For example, when the patient is pregnant, has viral hepatitis, hereditary hyperthyroidism, or takes certain medications (such as oral contraceptives), the thyroid binding globulin in the blood will increase significantly, resulting in a false increase in the test results.

When patients have hypoproteinemia, hereditary thyroid-binding globulin deficiency or take certain medications (such as estrogen, glucocorticoids, growth hormone, etc.), the thyroid-binding globulin in the blood will be significantly reduced, resulting in a falsely low test result.

In short, if there are certain abnormalities, it does not mean that there are abnormalities in thyroid function.

Therefore, in general, when doing initial screening, physical examinations, etc., it is sufficient to check three items.

For some patients who have abnormal thyroid function when they first see the doctor, such as patients with Hashimoto's thyroiditis who have been diagnosed with hyperthyroidism, hypothyroidism or are in the hyperthyroidism or hypothyroidism stage, and patients who have undergone partial or complete thyroidectomy and have been taking Euthyrox to supplement thyroid hormone, doctors usually ask patients to check five thyroid function tests.