1.Total triiodothyronine (TT3)
TT3 is the main hormone for the action of thyroid hormones on various target organs. TT3 is an important indicator for identifying early hyperthyroidism and monitoring recurrent hyperthyroidism. TT3 measurement can also be used to identify T3 hyperthyroidism and diagnose pseudo-thyrotoxicosis.
Increased: hyperthyroidism, hyperTBGemia, medically induced hyperthyroidism, TT3 is relatively increased during hyperthyroidism treatment and early hypothyroidism; TT4 may be decreased in patients with iodine deficiency goiter, but TT3 is normal and also relatively increased; T3 hyperthyroidism, some hyperthyroid patients have normal TT4 concentration, TSH is decreased and TT3 is significantly increased. Decrease: hypothyroidism, low T3 syndrome (seen in various serious infections, chronic heart, kidney, liver and lung failure, chronic wasting disease, etc.), low TBGemia, etc.
Normal reference value: 0.45~1.37ng/ml
2.Total thyroxine (TT4)
TT4 is the main product of thyroid secretion and an indispensable component of the integrity of the hypothalamic-pituitary-thyroid regulatory system. TT4 measurement can be used for the diagnosis of hyperthyroidism, primary and secondary hypothyroidism and monitoring of TSH suppression therapy.
Increased: hyperthyroidism, hyperTBGemia (pregnancy, oral estrogen and oral contraceptives, familial), acute thyroiditis, subacute thyroiditis, acute hepatitis, obesity, thyroid hormone application, consumption of thyroid tissue rich in thyroid hormones, etc. Decrease: Hypothyroidism, hypotBGemia (nephrotic syndrome, chronic liver disease, protein-losing enteropathy, hereditary hypotBGemia, etc.), total hypopituitarism, hypothalamic lesions, strenuous activity, etc.
Normal reference value: 4.5 to 12ug/dl
3.Free triiodothyronine (FT3)
FT3 and FT4 are the physiologically active forms of T3 and T4, and are a true reflection of the metabolic state of the thyroid gland. FT3 and FT4 are more sensitive and meaningful than T3 and T4. FT3 and FT4 have the advantage of not being affected by changes in their binding protein concentration and binding characteristics, and therefore do not require additional measurement of binding parameters.
FT3 content is important for the differential diagnosis of normal, hyper or hypothyroidism, and is sensitive for the diagnosis of hyperthyroidism, and is a specific indicator for the diagnosis of T3 hyperthyroidism.
4.Free thyroxine (FT4)
FT4 measurement is an important part of routine clinical diagnosis and can be used as a monitoring tool for thyroid suppression therapy. When thyroid dysfunction is suspected, FT4 and TSH are often measured together.
The triple test of TSH, FT3 and FT4 is commonly used to confirm hyperthyroidism or hypothyroidism, as well as to track the effectiveness of treatment.
Normal reference value: FT31.45~3.48pg/mlFT40.71~1.85ng/dl
5.Thyroid stimulating hormone (TSH)
TSH test is the primary screening test to identify thyroid function. A small change in free thyroid concentration brings about a significant adjustment in TSH concentration in the opposite direction. Therefore, TSH is a very sensitive and specific parameter for testing thyroid function and is particularly suitable for early detection or exclusion of dysfunction of the central hypothalamic-pituitary-thyroid regulatory loop.
Serum TSH is elevated in patients with TSH-secreting pituitary tumors, and TSH is an important indicator for monitoring thyroid cancer after surgery or after radiation therapy using thyroxine suppressive therapy.
Increased: primary hypothyroidism, ectopic TSH secretory syndrome (ectopic TSH tumor), pituitary TSH tumor, recovery from subacute thyroiditis. Decreased: Secondary hypothyroidism, tertiary (hypothalamic) hypothyroidism, with the exception of those due to hyperthyroidism CTSH tumor, and low measured values in those with EDTA anticoagulation.
Normal reference value: 0.49~4.67mIU/L
6.Anti-Thyroglobulin antibody (Anti-TG, TGA)
Thyroglobulin (TBG) is a potential auto-antigen that stimulates the body to produce TGA when it enters the bloodstream, which is the first auto-antibody found in thyroid disease and is highly species-specific and a common indicator for diagnosing autoimmune thyroid disease (AITD).
Elevated TGA concentrations can be found in patients with autoimmune thyroiditis and occur about 70-80% of the time. 60% of Graves’ disease is positive for TGA, and a decrease in titers after treatment indicates effective treatment. A positive TGA with high titer in hyperthyroidism indicates that anti-thyroid medication is ineffective and prone to recurrence after stopping medication. There is a correlation between thyroid cancer and TGA, and the positive rate can reach 13%-65%. An increase in TGA value is a sign of tumor deterioration.
Normal reference value: 0~34IU/ml
7.Anti-Thyroid microsomal antibody (Anti-TM, TMA)
TMA is one of the autoantibodies caused by autoimmune thyroid disease, and has been recognized as an important marker in the autoimmune process of the thyroid gland, like TGA. It is the most representative antibody and an indispensable indicator for the diagnosis of autoimmune thyroid disease, and is one of the specific means of diagnosing autoimmune thyroid disease in addition to histology.
In autoimmune thyroiditis (i.e. Graves’ disease), serum TGA and TMA are significantly higher than in normal subjects and other non-autoimmune thyroid diseases, and are of great value in the differential diagnosis of autoimmune thyroiditis, with a diagnostic compliance rate of up to 98% when the two are combined.
Serum TMA and TGA are significantly higher than normal in patients with immune diseases such as Hashimoto’s thyroiditis, primary hypothyroidism and hyperthyroidism, especially in Hashimoto’s thyroiditis, and serum TMA and TGA are “specific indicators” for the diagnosis of these diseases.
Both TMA and TGA are “specific indicators” for the diagnosis of these diseases. ① Hyperthyroidism: TGA and TMA are strongly positive, TMA is higher than TGA, and both antibodies are lower than Hashimoto’s thyroiditis. Some patients may turn negative for TGA and TMA after treatment, but most clinically cured hyperthyroid patients are weakly positive for TGA and TMA for a long time. Therefore, thyroid function should be reviewed regularly to prevent recurrence.
Hashimoto’s thyroiditis and Addison’s disease: TGA and TMA are strongly positive, while some patients are strongly positive for TMA and weakly positive or negative for TGA. The two antibodies are significantly higher than normal in patients with subthyroiditis and lower than in Hashimoto’s thyroiditis.
③Primary hypothyroidism: TGA and TMA are positive, but secondary hypothyroidism TGA and TMA are negative, to identify secondary hypothyroidism.
④Thyroid cancer: TGA is increased significantly.
⑤ Autoimmune disease during pregnancy: TGA and TMA can be increased.
Normal reference value: 0~50IU/ml
8.Anti-Thyroid peroxidase antibody (Anti-TPO, TPOA)
TPOA is the main thyroid tissue autoantibody, which is a key enzyme in the process of thyroid hormone synthesis and is closely related to immune damage to thyroid tissue. They mainly include thyroid-stimulating antibodies (TS-Ab) and thyroid-stimulating-blocking antibodies (TSB-Ab).
TPOA directly counteracts thyroid peroxidase (TPO), which catalyzes the iodination of thyroglobulin tyrosine during the biosynthesis of T3 and T4. Recent studies have confirmed that TPO is the main component of thyroid microsomal antigens and that TPOA is the active component of TMA, so the TPOA present in the patient is TMA.
TPOA is closely related to the occurrence and development of autoimmune thyroid disease (AITD), and can cause autoimmune-related hypothyroidism through cell-mediated and antibody-dependent cytotoxic effects that result in insufficient secretion of thyroid hormones. As a diagnostic and monitoring indicator of autoimmune thyroid disease, TPA has better sensitivity, specificity, reliability and significance than TMA, and has become the preferred indicator for the diagnosis of thyroid disease.
The main clinical applications of TPOA are: diagnosis of Hashimoto’s disease (HD) and autoimmune hyperthyroidism; toxicity of diffuse goiter (Graves); monitoring the effect of immunotherapy; detecting the possible development of familial thyroid disease; predicting the occurrence of postpartum thyroid dysfunction in pregnant women.
In patients with primary hypothyroidism, in combination with elevated TSH, early hypothyroid patients can be detected. In patients with suspected hypothyroidism, if TPOA is elevated, it can help to differentiate primary and secondary hypothyroidism. in patients with HT, TPOA is present throughout life, and if the clinical presentation is typical and TPOA is persistently high, it can be used as a diagnostic basis to confirm the diagnosis.
For patients with indications for thyroid hormone replacement therapy, including elevated TSH levels and positive anti-thyroid peroxidase TPOA, combined clinical testing for TPOA and TGA is used to identify the effects of immunotherapy, to identify the likelihood of disease in individuals with familial thyroid disease, and to predict the onset of postpartum thyroid dysfunction in pregnant women.
Testing for TPOA can help to solve clinical diagnostic challenges, such as abnormally high TSH levels accompanied by normal levels of free T4 (FT4), and if TPOA is elevated, subclinical hypothyroidism and early chronic lymphocytic thyroiditis should be considered. Low levels of TPOA account for 10% of asymptomatic patients and indicate a predisposition to thyroid autoimmune disease; 85% of patients with hyperthyroidism and hypothyroidism show high levels of TPOA, so the combined TPOA and TGA test has a higher clinical value in the diagnosis of most thyroid autoimmune diseases.
In addition, TPOA can be positive in patients with postpartum thyroiditis, atrophic thyroid, and some patients with nodular goiter; TPOA can be elevated in certain autoimmune diseases such as rheumatoid disease and systemic lupus erythematosus.
Normal reference value: 0 to 12 IU/ml
9.Thyroglobulin (TBG)
TBG is considered to be a special marker of the morphological integrity of the thyroid gland, and damage to the thyroid follicular wall can lead to a large amount of TBG entering the bloodstream.
In patients with congenital hypothyroidism, detection of TBG can identify complete thyroid deficiency, hypoplasia, or other pathological conditions. TBG determination can be used to identify subacute thyroiditis from pseudothyroidism, which has low TBG levels due to suppression of TSH.
TBG can be used for the observation and follow-up of the efficacy of hyperthyroidism. TBG is elevated in Graves’ disease, and TBG decreases normally after the remission of hyperthyroidism, and increases again when the symptoms worsen or recur; it can also be used for the diagnosis and observation of the efficacy of subacute thyroiditis (subthyroiditis), and blood TBG is elevated in subthyroiditis, and TBG decreases after treatment. TBG can also be used as an indicator for the prevention and monitoring of iodine-deficient goiter.
As a differentiation indicator of benign and malignant thyroid tumors, blood TBG is elevated in thyroid cancer (nail cancer), while normal or mildly increased in thyroid adenoma and cyst. When blood TBG is <20ug/L, nail cancer is less likely; >60ug/L, suggesting nail cancer; 20-60ug/L suggests residual cancer tissue or metastasis of nail cancer after surgery. In thyroid malignant tumors, the degree of elevation is related to the size and differentiation of the tumor and distant metastasis.
Since TBG is found to be elevated in varying degrees in both benign and malignant thyroid diseases, TBG testing is not helpful for the diagnosis and differential diagnosis of thyroid cancer, but TBG can return to normal after radical surgery for non-thyroidal diseases or thyroid diseases. Therefore, from the clinical practical aspect, TBG testing can be used as a simple means to identify, in addition to the follow-up of recurrence or not of highly differentiated nail cancer after surgery The TBG test can be used as a simple tool to identify whether a neck mass is caused by the thyroid gland or a metastatic tumor of thyroid origin.
Currently, TBG testing is mainly used for postoperative follow-up of differentiated thyroid cancer. It is a good indicator for treatment monitoring. In differentiated thyroid cancer, elevated TBG is usually caused by abnormal release of tumor tissue itself. A high TBG after lobectomy often indicates that the primary site of residual or metastatic cancer may be the thyroid gland, which is of great clinical significance for the treatment monitoring of differentiated thyroid cancer.
The presence of anti-thyroglobulin antibodies (TGA) in human body may lead to erroneous results in TBG determination, so clinicians should know the situation of TGA in patients.
Normal reference value: 5~40ug/L
10.Calcitonin (CT)
CT is a single-chain polypeptide hormone synthesized and secreted by C cells of thyroid follicular cells, also known as thyrocalcitonin. CT must be elevated in patients with medullary thyroid carcinoma because the half-life of calcitonin is short. Therefore, calcitonin can be used as an important marker for the diagnosis of thyroid tumors, observation of clinical efficacy, and indication of the presence or absence of tumor remnants or recurrence.
CT can also be used for examination of patients’ families as a monitoring of susceptibility in the family.
Patients with lung cancer, breast cancer, gastrointestinal cancer and pheochromocytoma may have increased serum CT due to high blood calcium or ectopic secretion. In addition, patients with liver cancer and cirrhosis may also occasionally have increased serum CT.
Normal reference value: 0~100ng/L
11.Thyroxine binding power (T-up, thyroid uptake test)
Measurement of thyroxine levels is an important tool to identify normal or abnormal thyroid function. Most of the thyroxine is bound to its transport protein, and the bound and free portions are in equilibrium. In many cases, although the free thyroxine is in the normal range, changes in the content of the transport protein can lead to changes in the total thyroxine measurement. Therefore, the determination of total thyroxine can only provide accurate information if T-uptake is normal.
T-uptake measurement gives an idea of the number of thyroxine binding sites. The free thyroxine index (FT4I), derived from the quotient of total thyroxine T4 and TBI (thyroxine binding index, = result of T-uptake measurement), reflects the two factors of variation: the content of transported proteins and the content of thyroxine.
Normal reference value: 0.66 to 1.27 TBI
12.Parathyroid hormone (PTH)
PTH is synthesized by the parathyroid glands and secreted into the bloodstream. It interacts with calcitonin to maintain the stability of blood calcium levels, while elevated blood calcium inhibits PTH secretion and lower blood calcium promotes PTH secretion.
Elevated blood calcium inhibits PTH secretion, while lower blood calcium promotes PTH secretion. Parathyroid disorders can cause changes in PTH secretion, which can lead to increased or decreased blood calcium levels (hypercalcemia or hypocalcemia). Parathyroid adenomas can cause hyperparathyroidism, which can lead to an increase in PTH secretion, so measuring PTH before and after parathyroid adenoma removal surgery can help surgeons understand the effects of the surgery.