1.What are the five items of thyroid function?
The five tests of thyroid function, namely TT3, TT4, FT3, FT4 and TSH, are commonly used to evaluate thyroid function.
TT3 serum total triiodothyronine, FT3 free triiodothyronine; TT4 serum total thyroxine, FT4 serum free thyroid hormone; TSH thyrotropin; TRH thyrotropin-releasing hormone.
Thyroxine is a tetraiodine-containing thyroid proline, which binds to thyroid binding protein to form T4 and free to form FT4, both of which are interconvertible and sum to TT4. TSH stimulates T4 secretion, and T4 can negatively inhibit TSH release; T4 is deiodinated to T3, which binds to TBG to form bound T3 or exists free to form FT3. TSH stimulates T3 secretion and T3 can negatively inhibit TSH release.
The prevailing view of the five A-factors.
The reason for this question is that this is a basic topic for testing A gong and an old one. Since it can be an old topic, it must represent its two characteristics: importance and ambiguity.
The current mainstream view is to use FT3 and FT4 as diagnostic criteria for perhaps the following reasons.
Because TT3 and TT4 are total thyroxine levels, which are affected by many factors, especially TBG; while FT3 and FT4 are free thyroxine, which have relatively less influence.
Even if the TBG is normal, TT4 and TT3 are purely to increase the financial burden of the patient, checking FT4 and FT3 is sufficient.
The “total” theory PK “free” theory refers to the 14th edition (latest version) of Practical Internal Medicine.
1. TT3 measurement is one of the most sensitive indicators for the diagnosis of hyperthyroidism.
In hyperthyroidism, serum TT3 can be four times higher than normal, which makes it easier to distinguish hyperthyroidism from normal people. However, this measurement is easily affected by changes in blood TBG concentration, so more attention should be paid when determining the results. For example, if TBG increases during pregnancy, TT3 may also increase. This is particularly important when determining the functional status of the thyroid gland and the dosage of medication for patients with hyperthyroidism combined with pregnancy.
2. FT3 is very sensitive for the diagnosis of hyperthyroidism.
However, the presence of autologous thyroid antibodies can interfere with FT3 and FT4 results.
(1) FT4 will be elevated when endogenous T4 antibodies are present in the blood.
(2) FT3 is elevated when endogenous T3 antibodies are present. In this case, a TRH excitation test, etc., is required to help further determine this.
As you can see, both TT3, TT4 and FT3 and FT4 are affected. Adherence to the “total” or “free” theory should be combined with clinically relevant indicators.
Some clinical recommendations.
1. Considering the effect of TBG on TT4 and TT3 in serum, it is recommended to add TBG test to facilitate comprehensive analysis to determine whether TT4 and TT3 elevation is false.
2, clinically you can also consider adding a thyroid stimulating antibody to assist in the determination.
3, thyroid-related disease diagnosis should not rely entirely on test data, the most important thing is to take a detailed medical history, physical examination, and clarify the relevant clinical symptoms.
4.At present, TT4 is an extremely critical indicator for reacting to the disease and adjusting the medication. When TT4 drops to the normal range or drops significantly, drug reduction is more reliable, while FT4 is prone to relapse or fluctuation even if it drops.
5, for a comprehensive assessment of thyroid function, it is recommended that 5 indicators should still be checked together.