Diagnostic criteria for neonatal hypothyroidism

After the baby is born, a series of examinations will be conducted. Parents cannot understand some of the examination data at all and need the doctor’s explanation to understand them. Below are the diagnostic criteria for neonatal hypothyroidism. Parents can learn about them and see which data are the main and key data so that they can take better care of their baby and fully understand the baby's condition at every stage during the baby's physical examination.

The specific diagnostic reference standards are as follows:

Primary hypothyroidism: TSH greater than 9mIU/L, FT4 less than 0.6ng/dl.

Primary subclinical hypothyroidism: TSH greater than 9mIU/L, FT4 normal (0.9-2.3ng/dl).

TBG deficiency: TSH normal (less than 9mIU/L); FT4 normal (0.9-2.3ng/dl); TT4 decreased (less than 5ug/dl); T3RUR greater than 45%.

Central hypothyroidism: TSH is less than 9mIU/L or normal; FT4 is decreased (less than 0.6ng/dl); TT4 is decreased (less than 5ug/dl).

This standard is formulated based on the reference value for newborns about two weeks after birth. When clinical physicians make judgments, they should fully consider the normal value range for each age group and the impact of different laboratory measurement reagents and methods. (The diagnostic criteria are determined by local laboratories based on their own reference values)

Once the diagnosis of congenital hypothyroidism is confirmed, further examination of the cause is required. For example, primary hypothyroidism requires thyroid B-ultrasound, thyroid scan, serum Tg and thyroid blocking antibody testing.

Central hypothyroidism requires TSH beta gene analysis, TRH receptor gene analysis, other pituitary hormone measurements, MRI examination of the optic nerve and hypothalamus-pituitary gland, etc.

1. General examination

① Routine blood tests often show mild to moderate anemia, which is normocytic normochromic, microcytic hypochromic or macrocytic.

② Normal or low blood sugar, flat glucose tolerance curve

③Increased blood cholesterol, triglycerides and β-lipoprotein.

2. Thyroid function test: ① The basal metabolic rate is reduced, usually below -30% to 45%; ② The thyroid iodine uptake rate is lower than normal, showing a flat curve; ③ The serum T4 is reduced, usually below 38.6nmol/L (30ng/ml), and FT4 is often <9.11pmol/L (7.08pg/ml); serum T3 and FT3 may also be reduced to varying degrees, but sometimes they can be normal in mild to moderate patients, and serum rT3 may be lower than 0.3nmol/L (0.2ng/ml).

4. X-ray examination, CT, MRI or ventriculography of the skull should be performed to exclude pituitary tumors, hypothalamic tumors or other intracranial tumors that may cause hypothyroidism. In primary hypothyroidism, the pituitary gland and sella turcica may secondarily enlarge.

5. Thyroid autoantibody examination: For patients whose etiology is related to thyroid autoimmunity, anti-thyroid microsomal antibodies (TMA) and anti-thyroglobulin antibodies (TGA) in the patient's blood may be elevated.

Auxiliary examination: For typical hypothyroidism patients, the diagnosis can be confirmed based on clinical symptoms and signs. For patients with atypical or more complicated conditions, laboratory tests are required to make a clear diagnosis. There are many examination items for patients with hypothyroidism, and each examination has certain clinical significance. It is very important to select some items for examination according to the different conditions of each patient.

In addition to clinical manifestations, the diagnosis of hypothyroidism is mainly established by testing TT4, FT4, TT3, FT3, TSH and TRH stimulation test.