Congenital hypothyroidism (CH) refers to a congenital disorder caused by insufficient production of thyroid hormones or defects in their receptors, which is a common endocrine disorder in children. It is a common endocrine disease in children. Since most of the children with the disease have atypical clinical manifestations at birth, the delay in diagnosis will make the child untimely treated, and if the correct treatment with thyroid preparations is not detected and started in the neonatal period, it will lead to mental retardation of the child, which will affect the quality of life of the child in the future. For this reason, screening of newborns for CH has been performed in China since 1981 and was included in the Maternal and Child Health Act in 1995 as a legal screening for newborn diseases. Despite this, the overall coverage of CH screening in China is only 50-60% due to varying economic conditions in different regions. After more than 10 years of screening statistics, the prevalence of CH in China is about 1/2050, with more women than men (ratio 2:1). Typical manifestations mainly have the following characteristics: three super – overdue delivery, huge babies, prolonged neonatal jaundice period, three less – less movement, less food, less crying. Other features include: constipation, umbilical hernia, dry skin, large tongue and low nasal bridge. However, because the mother’s thyroid hormones pass through the placenta to protect the baby, the majority of babies with CH are born without significant abnormalities or even without symptoms. Because of this, screening of newborns for CH is an important measure for early diagnosis and treatment (screening for suspicion – confirmatory thyroid hormone testing – treatment after diagnosis). Neonatal screening In 2010, the technical specifications for screening newborns for disease were issued by the Ministry of Health, specifying the method of screening: 72 hours after birth and within 7 days of full-term newborns, with adequate breastfeeding, blood is collected from the heel and dripped onto a special filter paper sheet for determination of dried blood filter paper thyrotropin (TSH) levels. This method is simple, cost-effective, and sensitive in screening for primary hypothyroidism (lesions in the thyroid gland) and hyperTSHemia, but may be missed in children with central hypothyroidism (lesions in the hypothalamus) and delayed TSH elevation (e.g., critically ill infants, newborns receiving blood transfusions, low birth weight infants). Thus, even with newborn screening, approximately 5% of children with CH will not be screened using this method. Confirmatory testing When screening is abnormal, venous blood is collected again for detailed thyroid function tests, including serum FT3, FT4 and TSH, and when TSH is elevated and FT4 is decreased, CH is diagnosed; when FT4 is normal and TSH is elevated, hyper TSH is diagnosed. When both TSH and FT4 are lower than normal, it may be central hypothyroidism. Interpretation of results and treatment measures 1. When there is a positive value in the newborn screening test, i.e., when the TSH level is elevated above 15-20 mU/L (the upper limit of normal will vary depending on the laboratory), venous blood should be collected again for FT4 and TSH testing. If there is a decrease in FT4 levels and an increase in TSH levels, the diagnosis of congenital hypothyroidism is confirmed and levothyroxine tablets (L-T4) should be given for treatment. L-T4 replacement therapy should be started before the serum retest results are available to minimize the impact on the child’s neurological development in the following cases: when the TSH result is greater than 40 mIU/L at screening, or when the thyroid gland is found to be poor or absent on ultrasound, or when the TSH at screening is >10 mIU/L and the child has two or more clinical manifestations of hypothyroidism, or when there is a delayed appearance of the distal femoral ossification center. 2. When the TSH is >10mIU/L despite normal FT4 on venous blood retest (especially in children 2 weeks old and 2 to 20 weeks old with TSH values between 1.7 and 9.1mIU/L), this condition can be called hyper TSHemia and replacement therapy with L-T4 is currently favored. If not treated, then the child should have FT4 and TSH retested at weeks 2 and 4 thereafter to observe trends. If FT4 and TSH are still abnormal, then treatment should be given as soon as possible. 3. For those babies whose TSH is always 6-10mIU/L, there is controversy in the academic community about the management of this condition. Generally speaking, it is recommended that the child be closely followed up for thyroid function and perfected for thyroid ultrasound and bone age testing. How to take L-T4 Because current research suggests that the eventual intelligence level of children with CH is closely related to when they start replacement therapy, the dose, and how well they are maintained in the future (especially up to age 3), the earlier L-T4 replacement is given when CH is diagnosed, the better. Early doses should be sufficient to allow TSH and FT4 to return to normal within 2 weeks, and FT4 levels should be near the upper limit of normal values. Thereafter FT4 and TSH levels should be followed regularly and the L-T4 dose adjusted individually according to them. For small infants, when taking L-T4, the tablets should be crushed and fed with a small spoonful of milk or water, not in a large container such as a bottle, to avoid any deviation in the drug dose. Avoid taking the medication with soy milk, fruit, calcium tablets, iron, fiber, etc., as this will reduce the absorption and utilization of L-T4. Are there any side effects and can I stop taking it on my own? L-T4 for CH children is a replacement therapy and the dose of the drug is in accordance with physiological needs. It is the same as watering crops when they are dry and eating when people are hungry. Unless L-T4 is taken too much, then hyperthyroidism will occur, which is like watering the crops too much and waterlogging them, or eating too much and propping them up. Therefore, you cannot just stop taking the medication, and you have to review it regularly. If the thyroid gland is confirmed by ultrasound to be underdeveloped or absent, then thyroxine must be taken for life. In other cases, it is generally not recommended to stop taking thyroid medication under the age of three. After the age of three, you can try to stop the medication for one month and have your thyroid function rechecked. If it is still normal at that time, it is temporary hypothyroidism and can be stopped but must be followed closely. If TSH is elevated and FT4 is decreased again after 1 month off the medication, then you should also take the medication for life.