Interpretation of thyroid function report sheet and influencing factors of related index detection (full)

With the increase of abnormal thyroid indicators year by year, people have paid more and more attention to thyroid function in recent years, but as a complex human organ, the normal function of the thyroid gland is affected by many factors
。 In normal people, the hypothalamus secretes thyrotropin-releasing hormone (TRH), regulates the secretion of thyroid-stimulating hormone (TSH), TSH acts on the thyroid gland to promote thyroid secretion of thyroid hormone T3, T4, and in the process of thyroid hormone synthesis also requires thyroid peroxidase (TPO), thyroglobulin (Tg) and TSH receptor (TSHR) and other participation, when thyroid hormone reaches a certain concentration, This information is further transmitted to the hypothalamus and pituitary gland through feedback regulation, so that the entire thyroid system is maintained at a relatively stable level
.

Although the clinical detection of thyroid function mainly depends on TSH, T3, T4, TPOAb, TgAb, TRAb and other related indicators, in fact, the realization of normal thyroid function is more complicated, whether TSH and TSHR can be normally combined, whether thyroid tissue can normally secrete T3, T4, T3, T4 can be transported into cells and bound to peripheral binding proteins (TBG, ABL, etc.
), and whether inactive T4 can be converted to active T3.
Whether T3 can bind normally to the receptors of the target tissue and whether the hypothalamic-pituitary-target gland feedback mechanism is normal can affect the normal exertion of thyroid function, so thyroid function is far more complex than the problem reflected in the detection index
figures.

Without the interference of test factors, in the normal human body, free T4 (FT4) and TSH have a certain linear relationship, usually the higher the level of FT4, the lower the level of TSH, if the relationship between T4 and TSH level is out of the normal corresponding range, there are some changes in high and low, there are usually some basic laws that can attribute patients to a specific disease, as shown in the figure below
.
Thyroid function report sheet interpretation ideas

Thyroid secretion indicators

1.
Thyroxine

Includes total triiodothyronine (TT3), total thyroid hormone (TT4), free triiodothyronine (FT3), and free thyroxine (FT4).

It is an important hormone secreted by the thyroid gland, which has many functions
such as promoting nutritional metabolism, physical growth, brain development, and improving nerve and cardiovascular function.
The level of serum thyroxine directly reflects the functional status of
the thyroid gland.

Clinical significance

➤ Increased: indicates hyperthyroidism, seen in Gravse disease, thyroidemia in the early stage of thyroiditis, Hashimoto's hyperthyroidism and functional thyroid nodules, drug-induced hyperthyroidism (taking iodine-containing preparations, contraceptives, estrogen and taking thyroxine drugs for overdose, etc.
).

➤ Reduced: seen in primary hypothyroidism and secondary hypothyroidism (after treatment of hyperthyroid iodine 131, after thyroid surgery, pituitary hypothyroidism, drug-induced hypothyroidism, etc.
).

Among them, FT3 and FT4 are relatively stable and not susceptible to other factors, which are commonly used laboratory indicators
for the diagnosis of hyperthyroidism and hypothyroidism.
FT3 is first elevated in early or early stage of hyperthyroidism, which is of great significance for the diagnosis of hyperthyroidism, and FT4 is also increased in hyperthyroidism, but decreased first in hypothyroidism, which is better than FT3
in the diagnosis of hypothyroidism.

TT4 measurement can be used for the diagnosis of hyperthyroidism, primary and secondary hypothyroidism, and the monitoring of TSH suppressive therapy; 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%)
.
Changes in TT3 concentration indicate abnormal thyroid function, and TT3 and TT4 are often elevated
simultaneously in hyperthyroidism.
But there are exceptions
.

Special cases

➤Only increased TT3: including TT3 type hyperthyroidism (more common in iodine-deficient areas), TT3 dominant hyperthyroidism (that is, after hyperthyroidism is treated with drugs, TT4 has been normal, and TT3 continues to not decrease or even increase, this type has a high recurrence rate, suitable for surgical treatment), early hyperthyroidism or early stage of hyperthyroidism recurrence;

➤ Only TT4 increase: including TT4 type hyperthyroidism (related to eating too much iodine-containing food), a small number of elderly hyperthyroidism with only high TT4;

➤ Decreased TT4: seen in hypothyroidism
.

Therefore, TT3 and TT4 values
are often measured at the same time clinically.

2.
Calcitonin (CT)

It is a linear polypeptide hormone containing 32 amino acids secreted by parafollicular cells (also known as C cells) of the thyroid gland, and the main physiological function of calcitonin is to regulate the concentration of calcium ions in the blood, and maintain the balance
of calcium ions in the internal environment together with factors such as parathyroid hormone (PTH) and vitamin D.

The role of calcitonin

➤ The effect on bone: can weaken the activity of osteoclasts, enhance the activity of osteoblasts, thereby weakening the osteolysis process, enhancing the osteogenic process, reducing the calcium salt released by bone tissue, and increasing calcium salt deposition, so that blood calcium decreases
.
Calcitonin can also inhibit the dissolution and transfer of bone salts, inhibit the decomposition of bone matrix, and improve the rate
of bone renewal.

➤ Effects on the kidneys: Calcitonin can inhibit the reabsorption of calcium, phosphorus and sodium by the renal tubules, thereby increasing their excretion in the urine, reducing the concentration in the blood, causing hypocalcemia or hypophosphatemia, but has little effect on potassium and chlorine
.

➤ Effects on the gastrointestinal tract: It can inhibit the intestinal transport of calcium and the secretion
of gastric acid, gastrin and insulin.

Medullary thyroid cancer (MTC) originates from parafollicular cells of the thyroid gland and can secrete CT in large quantities, so CT is one of the most sensitive serological markers of MTC, and the measurement of CT is of great significance
for the diagnosis, preoperative and postoperative evaluation and management of MTC.

Clinical significance

➤CT screening in patients with thyroid nodules can diagnose MTC early, and serum calcitonin > 100 pg/ml without stimulation suggests the presence of MTC;

➤The level of preoperative CT is related to the degree of tumor malignancy, which can help determine the scope of surgery;

➤ Monitoring CT during postoperative follow-up can be used to predict recurrence risk and detect and manage metastases early
.

Indicators of TSH and TRH secretion

1.
TSH

TSH is produced in the pituitary gland and has the effect
of promoting the production of TT3, TT4, FT3 and FT4 by thyroid follicular cells.
Clinically, thyroxine secretion indexes and thyroid-stimulating hormone secretion indexes are often examined and considered together to reflect the secretion of the thyroid gland and guide the diagnosis and treatment
of thyroid diseases.

Clinical significance

➤TSH is controlled
by negative thyroxine feedback.
When thyroxine is high, TSH is low; When thyroxine is low, TSH is high
.
Therefore, TT3, TT4, FT3, FT4 are increased during hyperthyroidism, while TSH is reduced, and the opposite
is true when hypothyroidism.

➤Clinically, if only the increase and decrease of TSH, TT3, TT4, FT3, FT4 are normal, often diagnosed as subclinical hypothyroidism or hyperthyroidism
.

➤However, when serum free thyroid hormones (FT4, FT3) are higher than the normal range, but serum TSH is not suppressed, it indicates the possibility
of TSH adenoma.

2.
TRH

TRH is synthesized and secreted
by some nerve cells in the paraventricular nucleus of the hypothalamus.
It is transported to the pituitary gland through the pituitary portal system, which has the effect of promoting TSH secretion by the pituitary gland, which in turn affects the secretion
of thyroxine.

Clinical significance

➤ Elevated: more common in primary hypothyroidism, Sheehan's syndrome, anterior pituitary hypofunction, application of norepinephrine, dopamine, antithyroid drugs, cold reactions, etc.
;

➤ Reduced: seen in hyperthyroidism, hypothalamic hypothyroidism, etc
.

Thyroid biochemical immunological indicators

1.
Thyroglobulin (TG)

Normal value reference value 5~40μg/L
.

Clinical significance

➤ TG elevation may occur in thyroid diseases (such as hyperthyroidism, toxic nodular goiter, subacute thyroiditis, and chronic lymphocytic thyroiditis);

➤TG is of great significance for the prognosis judgment and monitoring of the treatment effect of thyroid cancer (DTC): clinical follow-up of DTC patients found that the sensitivity of measuring TG content to diagnose DTC recurrence or metastasis was 88%~97%, and the specificity was 100%; High preoperative TG levels for thyroid cancer indicate that the tumor can produce TG, and postoperative TG can be used as a sensitive follow-up tumor marker
.

2.
Thyroid autoantibodies

The three indexes of thyroid autoantibody endocrinology high-frequency examination were thyroid peroxidase antibody (TPO-Ab), thyroglobulin antibody (TG-Ab), and thyrotropin receptor antibody (TR-Ab).

(1) TPO-Ab and TG-Ab

These two antibodies are antibodies against thyroid cell contents, both of which are hallmark antibodies of autoimmune thyroiditis, may cause thyroid cell damage, and elevated levels indicate that thyroid tissue is in an active state of immune inflammation
.

TPO-Ab has essentially the same clinical significance as TG-Ab, but TPO-Ab is superior to TG-Ab in both sensitivity and specificity, and is the preferred indicator
for diagnosing thyroid autoimmune diseases, particularly Hashimoto's thyroiditis.
In contrast, TG-Ab is less specific, and elevated TG-Ab alone is of little diagnostic
significance.
In order to improve the positive detection rate, a combination of two antibodies is usually used
clinically.

Clinical significance

➤Etiological diagnosis: Significantly elevated TPO-Ab and TG-Ab are the main basis
for the diagnosis of Hashimoto's thyroiditis.
It can also be used to differentiate between autoimmune thyroid disease (AITD) and non-AITD, for example, primary hypothyroidism, which is positive for TPO-Ab and TG-Ab, and negative for secondary hypothyroidism
.
Patients with Graves disease with hyperthyroidism may also have elevated TPO-Ab and TG-Ab, but the degree is mild or TPO-Ab is elevated and TG-Ab is normal
.

➤Prognosis: It is generally believed that elevated TP-OAb and TG-Ab indicate an increased
risk of hypothyroidism in the future.
If TPO-Ab and TG-Ab are persistently positive in pregnant women, the risk of "postpartum thyroiditis" and "hypothyroidism in infants and young children" is high, but not absolute
.

➤TG-Ab can also be used as a monitoring index for differentiated thyroid cancer (TDC): under normal circumstances, TG-Ab levels in patients with differentiated thyroid cancer will gradually decrease after radical resection and turn negative within 1~4 years, if TG-Ab levels rise again, it often indicates tumor recurrence
.
Clinically, TG-Ab often combines TSH and TG for risk and prognosis assessment and treatment response monitoring before and after thyroid cancer
.

（2）TR-Ab

Antibodies against TSH receptors on the surface of thyroid cells, including thyroid-stimulating antibodies (TS-Ab) and thyroid-suppressive antibodies (TB-Ab) subtypes
.
The former is associated with the onset of autoimmune hyperthyroidism (i.
e.
, Graves' disease), while the latter is associated
with the onset of autoimmune hypothyroidism (e.
g.
, Hashimoto's thyroiditis).

At present, most hospitals only test TR-Ab and cannot detect the two subtypes
separately.
The clinically tested TR-Ab can be regarded as TS-Ab
.

Clinical significance

➤ Identification of the cause of hyperthyroidism: the positive rate of TR-Ab in patients with Graves' disease can reach more than 95%, while other causes of hyperthyroidism (such as subacute thyroiditis) are generally negative, so TR-Ab is often used to distinguish
Graves' disease from other thyroid diseases.

➤ Guide medication and judge prognosis: TR-Ab is an important reference indicator
to determine whether patients with Graves disease can stop taking drugs.
A positive TR-Ab indicates that the body is immunoactive, and a negative indicates that the body is in immune remission
.
If TR-Ab is also negative in patients with Graves disease after treatment and thyroid function returns to normal, it is unlikely to relapse after stopping the drug; If TR-Ab remains positive despite drug therapy, relapse after discontinuation is more
likely.

➤Helpful in predicting neonatal hyperthyroidism: TR-Ab can stimulate the fetal thyroid gland through the placenta, causing transient hyperthyroidism in newborns (incidence 1~2%)
.
Therefore, testing TR-Ab in pregnant women with Graves disease can help predict neonatal hyperthyroidism and guide whether aggressive screening or treatment is necessary
.

➤ Contribute to the diagnosis of Graves eye disease with normal thyroid function: Clinically, some exophthalmos patients, although the thyroid function is normal, but TR-Ab is strongly positive, this condition can also be diagnosed as Graves eye disease
.

TSH decreases and FT4/FT3 increases

TSH is low and FT4/FT3 is normal

TSH is normal or low and FT4/FT3 is low

TSH is elevated and FT4/FT3 is reduced

TSH is normal or elevated, and FT4/FT3 is elevated

TSH is normal, TT4/TT3 is abnormal and FT4/FT3 is normal

However, it is worth noting that combined with the clinical manifestations of patients, the combination pattern of different thyroid test results may usually correspond to multiple diseases, how to interpret the combination pattern of each thyroid test result? What diseases may be associated with abnormalities in these tests?

Common misinterpretation of thyroid function tests

Precautions for interpreting thyroid function reports

1.
Each thyroid function result can be caused by a variety of different diseases or clinical states, the same disease can present different forms of thyroid function at different stages of its occurrence and development, and sometimes only through numerical results without combining with clinical background may make wrong judgments
.
Clinically, pregnant women with severe early pregnancy reaction and vomiting often find a slight increase in FT4 and a mild decrease in TSH when testing thyroid function, and when clinically encountering this situation, do not rashly diagnose "Graves disease", but also think of "hCG-related hyperthyroidism during pregnancy (also known as 'pregnancy hyperthyroid syndrome')", which is related to
increased hCG production.
hCG is similar in structure to TSH, which can promote the secretion of thyroid hormones, resulting in a mild increase in FT4 and a mild decrease
in TSH.

If the pregnant woman has no previous history of hyperthyroidism, mild FT4 elevation and decreased TSH on thyroid work, negative thyroid autoantibodies such as TRAb and TPOAb, and significantly elevated hCG levels, it can be basically determined that it is "hCG-related hyperthyroidism during pregnancy"
.
Unlike Graves' hyperthyroidism, the course is transient and does not require antithyroid therapy
.

2.
Pregnancy and non-pregnancy thyroid function normal values are different, some physiological and hormone level changes that occur in the body during pregnancy will affect thyroid function, resulting in different thyroid function during pregnancy and non-pregnant period
.
The two most important hormones that affect thyroid function during pregnancy are human chorionic gonadotropin (hCG) and estrogen
.
In the first trimester, elevated hCG stimulates thyroid secretion, resulting in a slight decrease in thyroid-stimulating hormone (TSH) (called "subclinical hyperthyroidism") and a gradual return to normal TSH in the second and third
trimesters.

Estrogen increases serum levels of thyroid hormone-binding protein (TBG), and because 99% of thyroid hormone (TH) in the blood is bound to thyroid-binding protein, laboratory-measured total thyroid hormone (TT3, TT4) levels may be slightly elevated, while free thyroid hormones (FT3, FT4) usually remain normal
.
Therefore, in the early pregnancy laboratory laboratory function found a slight decrease in TSH, TT3, TT4 slightly increased, pregnant mothers do not need to worry, because this is not hyperthyroidism, but a normal physiological change
during pregnancy.

In 2011, the American Thyroid Association (ATA) guidelines first proposed the specific TSH reference value during pregnancy: first trimester (T1 stage) 0.
1~2.
5ml U/L; Second trimester (T2 stage) 0.
2~3.
0ml U/L; The third trimester (T3 stage) is 0.
3~3.
0ml U/L
.

The study of Professor Teng Weiping in China showed that the serum TSH level of Chinese groups was generally elevated, and the normal range of TSH during pregnancy proposed by ATA was not suitable for Chinese pregnant women, and it was recommended to use the pregnancy-specific TSH reference value in this region.
Hospitals that unconditionally obtain pregnancy-specific reference values can use the reference values
proposed in China's "Guidelines for the Diagnosis and Treatment of Thyroid Diseases in Pregnancy and Postpartum".

3.
Thyroid autoantibodies are not specific, thyroid autoantibodies (such as TPOAb, TGAb, etc.
) are mainly seen in various autoimmune thyroid diseases (AITD), and Graves hyperthyroidism, Hashimoto's thyroiditis, etc.
belong to the category of AITD, so these patients can detect thyroid autoantibodies, the difference between the two is: Hashimoto's thyroiditis patients have higher antibody titers, and Graves hyperthyroidism patients although TPOAb, TGAb, but antibody titers are relatively low
。

Because the diagnostic specificity of thyroid autoantibodies is not strong, and the antibody titer of the above two diseases does not have a sharp boundary, therefore, in clinical diagnosis, it is often combined with thyroid function, TRAb or thyroid fine needle aspiration cytology for comprehensive judgment
.

4.
HT is not always synchronized with changes in TSH, which is a sensitive indicator of thyroid functional activity, and TSH often precedes changes in TH when subclinical thyroid disease occurs, so the measurement of TSH is of great value
in the diagnosis of "subclinical hyperthyroidism" or "subclinical hypothyroidism".

The homeostasis of the hypothalamic-pituitary-thyroid axis is eventually achieved through feedback regulation between TH and TSH, but this requires a period of several weeks, during which the changes between TSH and T3 and T4 are not perfectly synchronized
.

In general, after hypothyroidism is replaced with TH preparation, it takes 4~6 weeks to return blood TSH to normal; After hyperthyroidism is treated with antithyroid drugs (ATD), it takes 2~6 months to restore blood TSH to normal range
.
Prior to this, the blood concentrations of T3, T4 and TSH will be contradictory, T3 and T4 are normal, and TSH is still elevated (hypothyroidism) or decreased (hyperthyroidism), which is the "non-equilibrium phase"
between TSH and TH.

This seemingly contradictory result is not that the laboratory test results are inaccurate, but that there is a time lag between the two to achieve a balance, which is of great significance
for evaluating the effect of medication in the "non-equilibrium period" and guiding clinical use.

In the absence of hyperthyroidism, FT3, FT4 increased, TSH decreased, after a period of treatment, FT3, FT4 has shown a downward trend, but TSH is still low, this stage of adjustment of drugs, can not only look at TSH, need to be based on FT3, FT4 and clinical experience and other comprehensive judgment
.

5.
TH decrease, not necessarily "hypothyroidism", generally speaking, when hypothyroidism, there is often a decrease in thyroid hormone (such as FT3, FT4) levels, but in turn, thyroid hormone levels decreased, must be hypothyroidism? The answer is: not necessarily
.

This is because the elderly, severely malnourished, and advanced cachexia patients often have a mild decrease in T3 (or T3, T4) during laboratory tests, while TSH is normal or mildly reduced, but T3 (rT3) is elevated
.
This condition is a protective response of the body to reduce metabolic consumption, clinically known as "low T3 syndrome", also known as "normal thyroid pathological syndrome" (ESS), and is not true hypothyroidism
.

6.
"Five Items" can assist in locating and diagnosis, and "hypothalamic-pituitary-thyroid" is one of the three most important endocrine axes of the
human body.
Thyroid secretion of TH is controlled by thyrotropin-releasing hormone (TRH) secreted by the hypothalamus and TSH secreted by the pituitary gland; At the same time, increased TH secretion can feedback inhibit the synthesis and secretion
of pituitary TSH.

Typically, feedback inhibition of TSH by TH prevails
.
In general, if TH and TSH change in opposite directions, it can be inferred that the primary lesion is in the thyroid gland (eg, Graves disease, high-functioning thyroid adenoma); When TH and TSH change in the same direction, it is possible (but not all) that the primary lesion is in the pituitary gland or hypothalamus
.

7.
Elevated TSH, TH ≠ pituitary hyperthyroidism, "pituitary hyperthyroidism" is hyperthyroidism caused by excessive TSH secretion, and the patient's TSH and TH are often elevated simultaneously; But conversely, TSH and TH are elevated at the same time, but not necessarily "pituitary hyperthyroidism", but also "resistance to thyroid hormone (RTH)"
.

Patients with RTH often have a family history, and "pituitary TSH tumors" usually have no family history, but TSH tumors in a small number of multiple endocrine adenomas (MEN-1 type) have familial onset;

Imaging of patients with RTH has no abnormal findings on the pituitary gland, and "pituitary TSH tumor" often finds adenomas;

In RTH patients, serum glycoprotein hormone α sub(α-GSU) levels decreased, and the pituitary TSH tumor α-GSU and/or α-GSU/TSH ratio was significantly increased;

Serum TSH response to TRH (thyroid-stimulating hormone-releasing hormone) is normal or enhanced, and the vast majority of patients with pituitary TSH tumor TSH do not respond to TRH;

Genetic testing found mutations in the gene encoding thyroid hormone receptor β (TRβ) that are most valuable
for diagnosing RTH.

8.
TSH has limitations in assessing thyroid function, TSH is the most sensitive indicator of thyroid function, especially in the diagnosis of subclinical hyperthyroidism or hypothyroidism
.
In addition, it is often used to diagnose central (including pituitary and hypothalamic) hypothyroidism: serum TSH should be greater than 10 mIU/L in primary hypothyroidism, and if TSH is normal or mildly elevated, "central hypothyroidism"
is suspected.

However, TSH also has certain limitations in reflecting thyroid function, and serum TSH should not be used as an indicator
to evaluate thyroid function for thyroid function abnormalities secondary to the pituitary gland or hypothalamus (i.
e.
, central hyperthyroidism or hypothyroidism) and thyroid hormone insensitivity syndrome (RTH).

9.
Mild increase in neonatal TSH≠ congenital hypothyroidism, normal full-term newborns TSH rapidly rises to 60~80mIU/L 30 minutes after birth, drops to 20mIU/L after 24 hours, and slowly drops to 6~10mIU/L
about 1 week after birth.
Newborn congenital hypothyroidism screening is mostly carried out 2~7 days after birth, heel blood TSH as long as it does not exceed 10mIU/L can be considered normal, can not be mechanically applied to adult hypothyroidism (TSH>5mIU/L) diagnostic criteria
.

Second, the influencing factors of laboratory indicators related to thyroid function

Different combinations of thyroid test results are very important for the diagnosis of the patient's disease state, in addition to the patient's own disease state will have a direct impact on the thyroid test index, the detection interference during the detection process and the patient's own disease history, diet level, medication status, etc.
may interfere with the detection index, therefore, when there is clinical doubt about the test results, it is particularly important to identify and confirm these interference factors to assist clinicians to make accurate judgments on the patient's disease state
。

What are the common factors that interfere with thyroid laboratory test indicators? How may these interfering factors trigger changes in thyroid-related laboratory parameters? What methods can be used to further exclude or confirm the presence of these influencing factors?

First, common physiological factors interfere

Biological variation

The intrapersonal variation of FT4 is relatively small, about 5%~7%, while TSH is relatively large in the individual, which can reach 29%, and its biological significance is to maintain the stability
of FT4 level.

Circadian rhythm

Studies have shown that subjects are sampled every 10 minutes, and the secretion curve of 24-hour TSH is drawn, and under the condition of uniform control of eating and sleeping time, all subjects have a significant circadian rhythm: high concentration levels at night, and low concentration levels during the day, and TSH levels in men at night are higher than women
.
Therefore, it is recommended to limit the blood collection time of thyroid function measurement, which should not be too broad, especially for patients after thyroid cancer surgery, pregnant women, subclinical hypothyroidism, etc.
, blood should be collected on an empty stomach in the early morning
.
But feeding and blood collection timing had little effect
on FT4 levels.

season

Studies by Japanese scholars have shown that TSH levels are low in summer and high in winter, but there are inconsistencies
in different literature.

pregnancy

Chorionic gonadotropin (HCG) caused by pregnancy has the effect of stimulating the thyroid gland, thereby inhibiting TSH secretion, reducing serum TSH levels by 20%~30%, hCG generally peaks at 8-10 weeks of pregnancy, usually HCG increases by 10000 IU/L, TSH decreases by 0.
1 mIU/L, so pregnant women are on average 0.
4 mIU/L lower than non-pregnant women, TSH level reduction occurs in 8-14 weeks of pregnancy, Decline is lowest between 10 and 12 weeks' gestation, and falls below
0.
1 mIU/L in 20% of pregnant women.

Treatment monitoring

A cross-sectional study showed that the incidence of undertreatment and overdose of levothyroxine (L-T4) was as high as 30%~50%, which had a great relationship
with the quality of L-T4 preparations, patient compliance, medication time, gastrointestinal absorption, and patients' personal constitution 。 In general, although TSH is a relatively sensitive measure of thyroid function, it also takes days or weeks to reach relatively stable levels, so FT4 levels may be more reliable; In addition, L-T4 is generally taken orally on an empty stomach, and T4 concentration rises fastest in the first 90 minutes and peaks at 2 hours, so routine monitoring should preferably perform sample collection and index testing
before taking the drug.

drugs

A variety of drugs including iodine-containing drugs and preparations used in cardiology and imaging, some antitumor drugs such as tyrosine kinase inhibitors sorafenib, imatinib, etc.
, and interferon α and other drugs immunotherapy may cause changes in thyroid function, so the influence
of these factors should be fully considered when diagnosing the patient's disease state.
Second, common measurement factors interference

Giant TSH

Giant TSH is an antigen-antibody complex formed by TSH autoantibody and TSH, its molecular weight is large, clearance in vivo is slowed down, its immunological activity is similar to monomer TSH, but the biological activity is low, and it can be combined with the antibody in the reagent during the determination process, resulting in increased measurement results, and the incidence of macro TSH in the population is 0.
6%~1.
6%.

Macro-TSH only interferes with the determination of TSH, so it may cause normal T3/T4, but TSH is mildly or significantly elevated, and PET precipitation and gel chromatography can be used to identify this population
.

Thyroid autoantibodies (THAAbs)

THAAbs is the body's own production of T3 / T4 antibodies, can exist in the body for months to years, in the general population THAAbs positive rate of about 1.
8%, autoimmune disease patients THAAbs positive rate up to 40%, THAAbs positive individual, TgAb / TPOAb positive rate as high as 80% ~ 100%, the presence of THAAbs in the body can bind to thyroid hormone analogues in the reagent, resulting in FT3/FT4 results falsely increased, When THAAbs interference is suspected, further identification and confirmation of interference is required, and the method of dilution and PEG precipitation is recommended for TT3/TT4 detection, and when FT3/FT4/TT3/TT4 needs to be detected at the same time, it is recommended to change the detection method for retesting or use the gold standard equilibrium dialysis-mass spectrometry method
.

Heterophile antibody (HA)

HA refers to immunoglobulins produced by known or unknown antigens that stimulate the production of immunoglobulins in the body that can bind to immunoglobulins of multiple species, the presence of HA in the body can last for 4-12 months, and can affect the determination
of neonatal thyroid hormones through the placenta.
When using the double antibody sandwich method, the probability of TSH interference caused by the presence of HA is greater, the probability of T3/T4 interference is small, and the incidence of interference with TSH determination is about 0.
4%, and the interference mainly leads to a false increase in detection indicators, so you can consider changing the detection method, dilution verification, or using heterophile antibody blocker (HBT) to exclude the presence of
HA.