1. Thyroid hormone-related thyroid disorders (1) Thyroid disorders with elevated TSH Recovery phase of normal thyroid function pathological syndrome When the body is in a systemic disease or severe disease will appear low T3 or low T4 syndrome. Once in the recovery phase of the disease, serum TSH will transition from the normal range to the elevated phase. As the disease fully recovers, serum TSH gradually falls back to normal. (2) Thyroid diseases with reduced TSH 1). Human chorionic gonadotropin (HCG) related thyrotoxicosis various physiological or pathological causes of increased HCG in the body, such as multiple pregnancies, chorionic carcinoma, gravida, there is an increase in HCG, because HCG has a TSH-like effect, resulting in an increase in serum thyroid hormone levels and a simultaneous decrease in TSH. 2). Other disease states or medications Causing a decrease in TSH Some diseases and medications can also cause TSH to fall below the lower limit of the normal range. One of the most common causes is an increase in cortisol. This can be caused either by the use of exogenous glucocorticoids or by an increase in endogenous cortisol, such as that caused by Cushing’s syndrome. 2, the application of laboratory tests in the diagnosis and treatment of thyroid disease recommendations (1) serum TSH levels have diurnal variation, with a peak at night, the lowest value is seen between 10:00 and 16:00, only 50% of the peak. (2) TSH levels are increased during childhood and by the use of certain drugs (e.g., pranolol); they are decreased during the first trimester of pregnancy and by the use of certain drugs (e.g., glucocorticoids, dopamine, phenytoin sodium, carbamazepine, and furosemide). (3) Because current assays cannot distinguish between the presence and absence of biologically active TSH isomers, TSH alone cannot be used to determine secondary hypothyroidism. Likewise, because the test is for the biologically inactive TSH isomer, the immunologically active TSH level is reported as normal, and central hypothyroidism is missed. (4) Choice of screening method for congenital hypothyroidism in parturient and prematurely discharged neonates: TSH rises rapidly and persists for 24 h after cutting the umbilical cord, whereas the onset and duration of the peak in premature infants may be delayed, and TSH results may be falsely elevated if tested within 24 h of the infant’s birth. When screening preterm infants, it is recommended that specimens be collected 2-4 weeks after birth, as the delayed TSH peak in some preterm infants may be due to immature pituitary-thyroid feedback mechanisms in preterm infants. The preferred TT4 method is advantageous in low birth weight infants or when screening is performed within the first 24 h of birth.