Thyroid disease is a common disease in endocrinology, the harm is greater, and it is very important to find and treat it in time. In the diagnosis and treatment of thyroid diseases, it is inseparable from various laboratory tests, and it can be said that thyroid-related laboratory tests are the "barometer" of everyone's thyroid health.
What are the common tests in the Barometer? What exactly does the test results represent clinical significance? What seems like a simple check is actually not simple ... Today, I will give you a one-time explanation.
Thyroid function tests
Thyroid function measurement is the most commonly used test for clinical evaluation of thyroid disease, including thyroid-stimulating hormone (TSH) and thyroxine (TH).
Generalized thyroxine includes total thyroxine (TT4), triiodothyronine (TT3), free triiodothyronine (FT3), and free thyroxine (FT4). Among them, TSH, FT3, FT4 detection is called three items of A gong, and TSH, TT3, TT4, FT3, FT4 test is called five items of A gong.
1. Thyroxine
Thyroxine is an important hormone secreted by the thyroid gland, which has many functions such as promoting nutrient metabolism, physical growth, brain development, improving nerve and cardiovascular function, and the level of its indicators directly reflects the functional state of the thyroid gland.
Normal reference values:
TT3 1.54~3.08nmol/L；TT4 4.5~12ug/dLl；FT3 4~10pmol/L ；FT4 10~31pmol/L 。
Elevated: indicates hyperthyroidism, seen in Gravse disease, early thyrotoxemia of methanitis, hashimoto hyperthyroidism and functional thyroid nodules, drug-induced hyperthyroidism, etc.
Decreased: Indicates hypothyroidism and is seen in primary and secondary hypothyroidism.
Among them, FT3 and FT4 are relatively stable and are not susceptible to other factors, and are commonly used laboratory indicators for diagnosing hyperthyroidism and hypothyroidism. FT3 is the first to rise in the early stages of hyperthyroidism or the beginning of recurrence, which is of great significance for the diagnosis of hyperthyroidism, while FT4 is also increased in hyperthyroidism, but it is the first to decrease in hypothyroidism, which is better than FT3 in the diagnosis of hypothyroidism.
TT4 is the main product of thyroid secretion and is an indispensable component of the integrity of the hypothalamic-anterior pituitary-thyroid regulatory system. The TT4 assay can be used for the diagnosis of hyperthyroidism, primary and secondary hypothyroidism, and for monitoring TSH suppression therapy.
TT3 is the main hormone that thyroid hormones act on various target organs, and the vast majority (99.5%) of TT3 in serum binds to specific proteins in plasma, and only a very small number are in a free state (0.5%). TT3 measurement is used for the diagnosis of early hyperthyroidism, T3 hyperthyroidism and pseudothyrotoxicosis, monitoring of recurrent hyperthyroidism and hypothyroidism, hypo-T3 syndrome, and diagnosis of hypo-TBGemia.
Clinically, TT3 and TT4 values are often measured at the same time, because TT3 and TT4 often rise simultaneously in hyperthyroidism, but there are exceptions:
Only TT3 is elevated, including TT3 hyperthyroidism (more common in iodine-deficient areas), TT3 dominant hyperthyroidism (i.e., hyperthyroidism has been normal after drug treatment, and TT3 continues to not decrease or even increase, this type of recurrence rate is high, it is advisable to treat surgically), hyperthyroidism or early recurrence of hyperthyroidism;
Only TT4 was elevated, including hyperthyroidism (associated with eating too much iodine-containing food) and a few older hyperthyroidism with only TT4.
2. Thyroid Stimulating Hormone (TSH)
TSH is produced in the pituitary gland and has the effect of promoting the production of thyroxine by thyroid follicular cells.
The determination of TSH is an important part of the examination of the hypothalamic-pituitary-thyroid regulatory axis, which is a very sensitive indicator of the normal function of the thyroid gland, as well as an important monitoring index of L-T4 suppression therapy after thyroid cancer surgery or radiation therapy, and an important monitoring index of pregnant thyroid disease.
Normal reference: 0.35 to 5 mIU/L (pregnancy exclusion)
Elevation: primary hypothyroidism, subclinical hypothyroidism, pituitary TSH tumor, recovery period of subacute thyroiditis, chronic lymphocytic thyroiditis, etc.
Decreased: hyperthyroidism, subclinical hyperthyroidism, tertiary (hypothalamic) hypothyroidism, drugs (glucocorticoids), Cushing syndrome, acromegaly, etc.
Since the level of TSH is controlled by the negative feedback of thyroxine, it is often considered in clinical practice and the thyroxine test index together to evaluate thyroid function and determine the cause of abnormal thyroid function. The table is as follows:
TSH and thyroxine test results
Thyrotropin-releasing hormone (TRH) test
Clinically, it is sometimes necessary to measure thyrotropin-releasing hormone (TRH), which has the effect of promoting the secretion of TSH by the pituitary gland, which in turn affects the secretion of thyroxine.
Elevated is more common in primary hypothyroidism, Sieghan syndrome, hypopituitar in the anterior pituitary gland, norepinephrine, dopamine, antithyroid drugs, cold response, etc.; decreased is common in hypothalamic hypothyroidism.
TRH measurement is required in patients with suspected primary hypothyroidism, Sieghan syndrome, anterior pituitary dysfunction, and hypothalamic hypothyroidism.
Calcitonin (CT) examination
CT is a hormone secreted by paraveal cells (also known as C cells) of the thyroid gland, the main physiological function is to regulate the concentration of calcium ions in the blood, together with parathyroid hormone (PTH) and vitamin D and other factors to maintain the balance of calcium ions in the internal environment.
Clinical significance:
Medullary thyroid carcinoma (MTC) originates from parathyroid cells of the thyroid gland and secretes CT in large quantities, so CT is one of the most sensitive serological markers of MTC, and ct measurement is important for the diagnosis, preoperative and postoperative evaluation and management of MTC:
CT screening of patients with thyroid nodules allows for early diagnosis of MTC, and serum calcitonin > 100 pg/mL without stimulation suggests the presence of MTC.
Preoperative CT level is related to the degree of malignancy of the tumor and can assist in determining the scope of surgery. Monitoring CT at postoperative follow-up can be used to predict the risk of recurrence, early detection and management of metastatic lesions.
Thyroid biochemical immune indicators examination
Clinically, for chronic lymphocytic thyroiditis (Hashimoto's thyroiditis), toxic diffuse goiter (i.e., Graves disease), thyroid tumors and pregnant women with abnormal thyroid function, the biochemical immune indicators of the thyroid gland need to be examined to further clarify the diagnosis and judge the prognosis, and the main test items and clinical significance are as follows:
1. Thyroglobulin (TG)
Normal value reference value: 5 ~ 40μg / L.
Thyroid disorders such as hyperthyroidism, toxic nodular goiter, subacute thyroiditis, and chronic lymphocytic thyroiditis can present with elevated TG;
The high preoperative TG level of differentiated thyroid carcinoma (DTC) suggests that the tumor can produce TG, and the postoperative TG can be used as a sensitive follow-up tumor marker, which is of great significance for the prognosis judgment and monitoring of the treatment effect of DTC.
2. Thyroid antibody
The commonly used thyroid autoantibody indicators are thyroid peroxidase antibody (TPO-Ab), thyroglobulin antibody (TG-Ab) and thyrotropin receptor antibody (TR-Ab).
TPO-Ab和TG-Ab
Antibodies to thyroid cell contents, which are hallmarks of autoimmune thyroiditis, may damage thyroid cells, and elevated levels indicate that thyroid tissue is in an active state of immune inflammation.
TPO-Ab is essentially the same clinical significance as TG-Ab, but TPO-Ab is more sensitive and specific than TG-Ab, and is the most sensitive indicator for diagnosing thyroid autoimmune diseases, especially Hashimoto's thyroiditis.
In contrast, TG-Ab is less specific, with only elevated TG-Ab having little diagnostic significance. In order to improve the positive detection rate, the two antibodies are usually tested in combination.
Diagnosis of etiology
TPO-Ab and TG-Ab are the differential diagnostic indicators for autoimmune thyroid disease (AITD), with the former being TPO-Ab and TG-Ab being multiple positive and the latter being negative.
Hashimoto's thyroiditis: significantly elevated TPO-Ab and TG-Ab is the main basis for diagnosing the disease.
Hyperthyroidism in Graves: elevated TPO-Ab, TG-Ab, but to a lesser extent, or elevated TPO-Ab and normal TG-Ab.
Prognosis
Hypothyroidism: elevated TPO-Ab and TG-Ab suggest an increased risk of future hypothyroidism.
PPT and infantile hypothyroidism: If pregnant women continue to be positive for TPO-Ab and TG-Ab, the risk of "postpartum thyroiditis" and "infantile hypothyroidism" is high, but not absolute.
Monitoring of DTCs
Normally, TG-Ab levels in patients with differentiated thyroid cancer gradually decrease after radical resection and turn negative within 1 to 4 years. If TG-Ab levels rise again, it often suggests a tumor recurrence.
Clinically, the results of TG-Ab, TSH and TG are often combined to assess the risks and prognosis of thyroid cancer before and after surgery, and to monitor the response to treatment.
TR-Ab
TR-Ab is an antibody against TSH receptors on the surface of thyroid cells, including two subtypes of thyroid-stimulating antibodies (TS-Ab) and thyroid inhibitory antibodies (TB-Ab).
The former is associated with the onset of autoimmune hyperthyroidism (e.g., Graves disease), while the latter is associated with the onset of autoimmune hypothyroidism (e.g., Hashimoto's thyroiditis).
At present, most hospitals only test for TR-Ab, and cannot test their subtypes separately. Clinically measured TR-Ab can often be thought of as TS-Ab.
Differentiate the cause of thyrotoxicosis
Guide medication and determine the risk of hyperthyroid recurrence
TR-Ab is an important reference indicator for determining whether patients with Graves disease can stop the drug. A positive TR-Ab often indicates that the body is immunocompetent, while a negative indicates an immune-remission state.
In patients with Graves disease, the nail function returns to normal after treatment, and if TR-Ab turns negative, the possibility of recurrence after discontinuation is small, and if TR-Ab is persistently positive, the possibility of recurrence after discontinuation is greater.
other
Predict neonatal hyperthyroidism: Testing TR-Ab in pregnant women with Graves' disease can help predict neonatal hyperthyroidism and guide treatment.
Helps diagnose Graves eye disease with normal thyroid function: Clinically, some patients with eye protrusions, although the thyroid function is normal, but TR-Ab is strongly positive, this condition can also be diagnosed as Graves eye disease.
It is worth noting that the greatest significance of clinical diagnostic detection of thyroid autoantibodies is to assist in clinical diagnosis, antibody titers can only be used as an important reference, the level of thyroid autoantibodies is not directly related to the severity of thyroid diseases, and the treatment goal of thyroid diseases is to correct thyroid function abnormalities, not to make antibodies negative.
Source: Lilac Garden Endocrine Time
Edited by: Yeah Reviewer: Xiao Ran