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*It is only for medical professionals to read and refer to the thyroid function test.
Don't just use it to judge hyperthyroidism/hypothyroidism.
These auxiliary effects are worth understanding! Thyroid function test is a commonly used clinical laboratory test, including total thyroxine (TT4), total triiodothyronine (TT3), free thyroxine (FT4), free triiodothyronine (FT3) and thyroid stimulating Element (TSH) level.
The basic purpose of thyroid function determination is to determine whether the thyroid function is in a "hyper" state or "decreased" state.
In fact, the use of thyroid function testing is more than that, it can also be used to evaluate other diseases and identify the cause of it! Assessment of health status There is an abnormal thyroid function.
It is not a disease of the thyroid itself, but a decrease in circulating thyroid hormone levels caused by severe diseases and starvation.
It is a protective response of the body.
This is a euthyroid sick syndrome ( ESS), also called low triiodothyronine (T3) syndrome, non-thyroid disease syndrome.
The mechanism is that the activity of type I deiodinase, which deiodinates the outer ring of thyroxine (T4) and converts it into T3, is inhibited, so the production of T3 is reduced and hypoT3emia occurs.
The characteristics of ESS laboratory examination are that serum FT3 and TT3 are decreased; TT4 is normal or slightly increased, and TSH is normal.
The severity of the disease is generally related to the degree of TT3 reduction.
In severe cases, TT4 and FT4 can be reduced, and TSH is still normal, which is called "low T3-T4 syndrome".
After the patient's underlying disease is recovered after treatment, thyroid hormone levels can gradually return to normal.
ESS does not require thyroid hormone replacement therapy.
If the patient is diagnosed with ESS, it indicates that there may be systemic diseases, including malnutrition, hunger, anorexia, diabetes, liver disease, etc.
, which is worthy of attention. Assessing the nutritional status of pregnancy, thyroid function has been used as a routine examination item during pregnancy.
If a pregnant woman is negative for thyroid autoantibodies, serum TSH levels are normal, and FT4 levels are lower than the lower limit of the specific reference range during pregnancy, it is called "simple hypothyroidism", also known as "hypothyroidism".
The effect of simple hypothyroidism on fetal development is still controversial.
Some studies believe that the disease can increase the risk of lower IQ, language delay, motor function decline, autism, and attention deficit/hyperactivity disorder in offspring.
Based on limited evidence, the American Thyroid Association (ATA) guidelines do not recommend levothyroxine (LT4) treatment for women with simple hypothyroidism, and domestic guidelines neither recommend nor oppose the administration of LT4 in early pregnancy.
Iodine deficiency is one of the causes of hypothyroidism.
Studies have shown that iron deficiency in early pregnancy is positively correlated with the reduction of FT4 levels, which is a risk factor for hypothyroidism.
Therefore, hypothyroidism during pregnancy may be a signal of iron deficiency, iodine deficiency, or iodine excess.
Find the cause and treat the cause.
Identifying the cause of thyrotoxicosis Thyrotoxicosis is a common clinical syndrome.
It is caused by various reasons to increase the thyroid hormones in the blood circulation, causing increased excitability and hypermetabolism in the nervous, circulatory, and digestive systems.
There are three main causes of thyrotoxicosis: ￭ Increased secretion of thyroxine synthesis: such as Graves disease, toxic thyroid adenoma, multinodular toxic goiter, pituitary thyroid stimulating hormone adenoma, etc.
; ￭ Thyroid cells are destroyed, thyroxine Release into the blood: such as painless thyroiditis (postpartum thyroiditis, etc.
), subacute thyroiditis, etc.
; ￭ Increased exogenous thyroxine: such as overdose of levothyroxine.
Identifying the above causes is the key to diagnosis and treatment of thyrotoxic symptoms.
Among them, Graves disease and destructive thyroiditis are common causes of endogenous thyrotoxicosis.
Thyroid autoantibodies, thyroid ultrasound, and thyroid iodine uptake rate/nuclide scan can assist in diagnosing the cause.
However, due to limited conditions, many grassroots units did not carry out these inspection items.
For the identification of the cause, the thyroid function test itself can also help "a hand.
"
Generally speaking, a high level of FT3 is a predictor of the severity of Graves’ disease, while destructive thyroiditis (such as painless thyroiditis) is manifested as a more significant increase in FT4 (because of the thyroid), because T4 is the main source of thyroid secretion hormone.
The 2016 version of the ATA "Guidelines for the diagnosis and treatment of thyrotoxicosis due to hyperthyroidism and other causes" recommends the use of the TT3/TT4 ratio to assess the cause of thyrotoxicosis: ①When the ratio of TT3/TT4 (ng/µg)>20, thyrotoxicosis The cause of the symptom is Graves’ disease or toxic nodular goiter; ②When the ratio of TT3/TT4 (ng/µg) is less than 20, the cause of thyrotoxicosis is considered postpartum thyroiditis, painless thyroiditis and other destructive thyroiditis.
It is worth noting that about 99.
97% of circulating T4 is combined with specific plasma proteins such as thyroxine binding globulin (TBG), and about 99.
7% of T3 is combined with TBG.
All factors that can cause changes in serum TBG levels can affect the determination results of TT4 and TT3, especially for TT4, such as pregnancy, viral hepatitis, hereditary TBG and certain drugs (estrogen, oral contraceptives) , Tamoxifen, etc.
) can increase TBG and cause false increases in TT4 and TT3 measurement results; hypoalbuminemia, hereditary TBG deficiency and a variety of drugs (androgens, glucocorticoids, growth hormones, etc.
) can reduce TBG, False reduction of TT4 and TT3 measurement results.
Therefore, comprehensive judgment is required when using the above ratio.
In 2005, an article published in Endocrine Journal pointed out that FT3/FT4 still has a lot of overlap in distinguishing painless thyroiditis from Graves’ disease, but when the value of FT4 increases significantly [>69.
7 pmol/L(5.
4 ng/dL)], there is a good FT3/FT4 cut point to distinguish painless thyroiditis (≤2.
4) from Graves disease (>2.
4).
The sensitivity of this cut point can reach 97% and the specificity can reach 75% . Summary Thyroid function test mainly reflects the state of thyroid function, but its role in evaluating other diseases or identifying the cause of thyrotoxicosis should not be underestimated.
If the value of thyroid function can be better utilized, it will reduce the burden on patients and medical resources.
References: [1] Ross DS, Burch HB, Cooper DS, et al.
2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and other causes of Thyrotoxicosis[J].
Thyroid, 2016: 2016, 26(10):1343 -1421.
[2] Chinese Medical Association Endocrinology Branch.
Guidelines for Diagnosis and Treatment of Thyroid Diseases in Pregnancy and Postpartum (Second Edition)[J].
Chinese Journal of Endocrinology and Metabolism, 2019, 35(8):636-665.
[3] Chinese Medicine Association of Endocrinology.
Guidelines for the diagnosis and treatment of adult hypothyroidism[J].
Chinese Journal of Endocrinology and Metabolism, 2017, 33(02): 167-180.
[4] Minasyan M, Dulęba A, Smalarz A, et al.
fT3:fT4 ratio in Graves' disease-correlation with TRAb level, goiter size and age of onset[J].
Folia Med Cracov, 2020, 60(2):15-27.
[5] Chiaki S, Kyoju A, Shin-Ichi T, et al.
Lower serum free thyroxine (T4) levels in painless thyroiditis compared with Graves' disease despite similar serum total T4 levels[J].
Journal of Clinical Endocrinology & Metabolism, 1987, 65(2):359-63.
[6] Yoshimura Noh J, Momotani N, Fukada S, et al.
Ratio of serum free triiodothyronine to free thyroxine in Graves' hyperthyroidism and thyrotoxicosis caused by painless thyroiditis [J].
Endocrine J, 2005, 52(5):537-542.
Don't just use it to judge hyperthyroidism/hypothyroidism.
These auxiliary effects are worth understanding! Thyroid function test is a commonly used clinical laboratory test, including total thyroxine (TT4), total triiodothyronine (TT3), free thyroxine (FT4), free triiodothyronine (FT3) and thyroid stimulating Element (TSH) level.
The basic purpose of thyroid function determination is to determine whether the thyroid function is in a "hyper" state or "decreased" state.
In fact, the use of thyroid function testing is more than that, it can also be used to evaluate other diseases and identify the cause of it! Assessment of health status There is an abnormal thyroid function.
It is not a disease of the thyroid itself, but a decrease in circulating thyroid hormone levels caused by severe diseases and starvation.
It is a protective response of the body.
This is a euthyroid sick syndrome ( ESS), also called low triiodothyronine (T3) syndrome, non-thyroid disease syndrome.
The mechanism is that the activity of type I deiodinase, which deiodinates the outer ring of thyroxine (T4) and converts it into T3, is inhibited, so the production of T3 is reduced and hypoT3emia occurs.
The characteristics of ESS laboratory examination are that serum FT3 and TT3 are decreased; TT4 is normal or slightly increased, and TSH is normal.
The severity of the disease is generally related to the degree of TT3 reduction.
In severe cases, TT4 and FT4 can be reduced, and TSH is still normal, which is called "low T3-T4 syndrome".
After the patient's underlying disease is recovered after treatment, thyroid hormone levels can gradually return to normal.
ESS does not require thyroid hormone replacement therapy.
If the patient is diagnosed with ESS, it indicates that there may be systemic diseases, including malnutrition, hunger, anorexia, diabetes, liver disease, etc.
, which is worthy of attention. Assessing the nutritional status of pregnancy, thyroid function has been used as a routine examination item during pregnancy.
If a pregnant woman is negative for thyroid autoantibodies, serum TSH levels are normal, and FT4 levels are lower than the lower limit of the specific reference range during pregnancy, it is called "simple hypothyroidism", also known as "hypothyroidism".
The effect of simple hypothyroidism on fetal development is still controversial.
Some studies believe that the disease can increase the risk of lower IQ, language delay, motor function decline, autism, and attention deficit/hyperactivity disorder in offspring.
Based on limited evidence, the American Thyroid Association (ATA) guidelines do not recommend levothyroxine (LT4) treatment for women with simple hypothyroidism, and domestic guidelines neither recommend nor oppose the administration of LT4 in early pregnancy.
Iodine deficiency is one of the causes of hypothyroidism.
Studies have shown that iron deficiency in early pregnancy is positively correlated with the reduction of FT4 levels, which is a risk factor for hypothyroidism.
Therefore, hypothyroidism during pregnancy may be a signal of iron deficiency, iodine deficiency, or iodine excess.
Find the cause and treat the cause.
Identifying the cause of thyrotoxicosis Thyrotoxicosis is a common clinical syndrome.
It is caused by various reasons to increase the thyroid hormones in the blood circulation, causing increased excitability and hypermetabolism in the nervous, circulatory, and digestive systems.
There are three main causes of thyrotoxicosis: ￭ Increased secretion of thyroxine synthesis: such as Graves disease, toxic thyroid adenoma, multinodular toxic goiter, pituitary thyroid stimulating hormone adenoma, etc.
; ￭ Thyroid cells are destroyed, thyroxine Release into the blood: such as painless thyroiditis (postpartum thyroiditis, etc.
), subacute thyroiditis, etc.
; ￭ Increased exogenous thyroxine: such as overdose of levothyroxine.
Identifying the above causes is the key to diagnosis and treatment of thyrotoxic symptoms.
Among them, Graves disease and destructive thyroiditis are common causes of endogenous thyrotoxicosis.
Thyroid autoantibodies, thyroid ultrasound, and thyroid iodine uptake rate/nuclide scan can assist in diagnosing the cause.
However, due to limited conditions, many grassroots units did not carry out these inspection items.
For the identification of the cause, the thyroid function test itself can also help "a hand.
"
Generally speaking, a high level of FT3 is a predictor of the severity of Graves’ disease, while destructive thyroiditis (such as painless thyroiditis) is manifested as a more significant increase in FT4 (because of the thyroid), because T4 is the main source of thyroid secretion hormone.
The 2016 version of the ATA "Guidelines for the diagnosis and treatment of thyrotoxicosis due to hyperthyroidism and other causes" recommends the use of the TT3/TT4 ratio to assess the cause of thyrotoxicosis: ①When the ratio of TT3/TT4 (ng/µg)>20, thyrotoxicosis The cause of the symptom is Graves’ disease or toxic nodular goiter; ②When the ratio of TT3/TT4 (ng/µg) is less than 20, the cause of thyrotoxicosis is considered postpartum thyroiditis, painless thyroiditis and other destructive thyroiditis.
It is worth noting that about 99.
97% of circulating T4 is combined with specific plasma proteins such as thyroxine binding globulin (TBG), and about 99.
7% of T3 is combined with TBG.
All factors that can cause changes in serum TBG levels can affect the determination results of TT4 and TT3, especially for TT4, such as pregnancy, viral hepatitis, hereditary TBG and certain drugs (estrogen, oral contraceptives) , Tamoxifen, etc.
) can increase TBG and cause false increases in TT4 and TT3 measurement results; hypoalbuminemia, hereditary TBG deficiency and a variety of drugs (androgens, glucocorticoids, growth hormones, etc.
) can reduce TBG, False reduction of TT4 and TT3 measurement results.
Therefore, comprehensive judgment is required when using the above ratio.
In 2005, an article published in Endocrine Journal pointed out that FT3/FT4 still has a lot of overlap in distinguishing painless thyroiditis from Graves’ disease, but when the value of FT4 increases significantly [>69.
7 pmol/L(5.
4 ng/dL)], there is a good FT3/FT4 cut point to distinguish painless thyroiditis (≤2.
4) from Graves disease (>2.
4).
The sensitivity of this cut point can reach 97% and the specificity can reach 75% . Summary Thyroid function test mainly reflects the state of thyroid function, but its role in evaluating other diseases or identifying the cause of thyrotoxicosis should not be underestimated.
If the value of thyroid function can be better utilized, it will reduce the burden on patients and medical resources.
References: [1] Ross DS, Burch HB, Cooper DS, et al.
2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and other causes of Thyrotoxicosis[J].
Thyroid, 2016: 2016, 26(10):1343 -1421.
[2] Chinese Medical Association Endocrinology Branch.
Guidelines for Diagnosis and Treatment of Thyroid Diseases in Pregnancy and Postpartum (Second Edition)[J].
Chinese Journal of Endocrinology and Metabolism, 2019, 35(8):636-665.
[3] Chinese Medicine Association of Endocrinology.
Guidelines for the diagnosis and treatment of adult hypothyroidism[J].
Chinese Journal of Endocrinology and Metabolism, 2017, 33(02): 167-180.
[4] Minasyan M, Dulęba A, Smalarz A, et al.
fT3:fT4 ratio in Graves' disease-correlation with TRAb level, goiter size and age of onset[J].
Folia Med Cracov, 2020, 60(2):15-27.
[5] Chiaki S, Kyoju A, Shin-Ichi T, et al.
Lower serum free thyroxine (T4) levels in painless thyroiditis compared with Graves' disease despite similar serum total T4 levels[J].
Journal of Clinical Endocrinology & Metabolism, 1987, 65(2):359-63.
[6] Yoshimura Noh J, Momotani N, Fukada S, et al.
Ratio of serum free triiodothyronine to free thyroxine in Graves' hyperthyroidism and thyrotoxicosis caused by painless thyroiditis [J].
Endocrine J, 2005, 52(5):537-542.
