Serum calcitonin is a hormone secreted by the follicular cells of the thyroid gland that, when elevated for some reason, increases renal excretion of calcium and lowers blood calcium concentrations. Endemic goiter is a type of goiter. So, what are the tests that patients with increased serum calcitonin levels need to do? The following is a brief introduction: Serum total T4 (TT4) measurement: 1, the principle of measurement: thyroxine (T4) from the thyroid gland into the circulating blood, immediately with the plasma protein binding (about 99.95%), only a very small amount (0.05%) is a free state and play a physiological role. The result of this assay, including the sum of bound and free proteins, reflects the total T4 concentration. It is usually measured by radioimmunoassay. 2, reference value 129 healthy adults (male 70, female 59) serum total T4 concentration of 106.8 ± 23.2nmol / L, the measured range of 54.1-1183.2nmol / L. 3, clinical significance: hyperthyroidism, serum total T4 concentration is higher than the upper limit of the normal range of untreated patients with hyperthyroidism, the serum total T4 concentration is significantly higher than the normal range, the average value is higher than the normal value of 2-135 nmol / L. The total T4 concentration of the serum total T4 concentration is higher than the normal value of 2-150 nmol / L, the total T4 concentration is higher than the normal value. In untreated hyperthyroidism, the serum total T4 concentration is significantly higher, the average value is 2-3 times higher than the normal value, and the diagnostic compliance rate is more than 95%. It is a sensitive diagnostic index for early and post-cure recurrence of hyperthyroidism, and can also be used to determine the state of thyroid function during the treatment of hyperthyroidism, to observe the efficacy of treatment, and to adjust the dosage of medication. The serum total T4 concentration of hypothyroid patients is lower than the lower limit of the normal range in most cases, and in a few cases, it crosses over with normal. Detection of serum total T4 is valuable in guiding the adjustment of dosage of alternative therapies in hypothyroid patients. Combined application with workup tests to diagnose neonatal hypothyroidism is an important research tool in eugenics both at home and abroad.