Serum calcitonin is a hormone secreted by thyroid follicular cells that, when elevated for some reason, increases the excretion of calcium by the kidneys and lowers blood calcium concentrations. Endemic goiter is a type of goiter. In the early stages, there are no obvious clinical symptoms. The thyroid gland is mildly to moderately diffusely enlarged, soft and painless. Very few significantly enlarged cases may show symptoms of pressure, such as dyspnea, dysphagia, hoarseness, and irritating cough. A retrosternal goiter may have symptoms of esophageal or superior vena cava compression. So, what tests should be done when a patient has an increased serum calcitonin level? The following is a brief introduction: 1, calcitonin, calcitonin is a disulfide peptide containing a disulfide bond, molecular weight of 3400. normal human serum calcitonin concentration is 10-20ng/L, plasma half-life is less than 1h, mainly in the kidney degradation and excretion. The main role of calcitonin is to reduce blood calcium and blood phosphorus, its main target organ is bone, and also has a certain effect on the kidney. 2. Determination of the rate of iodine uptake by the thyroid gland: The thyroid gland has the ability to take in and concentrate iodine ions, and the amount and rate of iodine ions it absorbs is closely related to its functional state. In hyperthyroidism, the rate of 131 iodine uptake is high and fast. When the thyroid gland is hypothyroid, the rate of 131 iodine uptake is low and slow. The measurement of the 131 iodine uptake rate of the thyroid gland is of high value in determining the functional status of the thyroid gland. The thyroid aspiration 131 iodine test is the most effective method for clinical application of radioactive iodine to check thyroid function. Because of its easy method and high accuracy, it has become a routine test for checking the function of inorganic iodine uptake by the thyroid gland in most clinical units. At present, the measurement methods used, the size of the tracer, etc. are very different, and the diagnostic criteria are also different. The amount of tracer can range from l-2 microcuries to tens of microcuries (1Ci=3.7 × 1010Bq). The detection techniques include direct measurement, where the counting tube is placed directly on the thyroid gland, and remote measurement, where the scintillation probe or Y-counting tube is placed at a certain distance from the neck. Proximity direct measurement method. The results of the measurement are generally based on a 24h thyroid iodine uptake rate of 15%-45% as the normal range, with less than 15% as low function and more than 45% as higher than normal.