Reduced secretion of antidiuretic hormone (adh) is one of the symptoms of syndrome of inappropriateantidiuretic hormone secretion (SIADH), a 9-peptide hormone secreted by nerve cells in the supraoptic and paraventricular nuclei of the hypothalamus. hormone, which is released after reaching the pituitary gland via the hypothalamic-pituitary bundle. Its main role is to increase the water permeability of the distal convoluted tubules and collecting ducts, promote water absorption, and is a key regulatory hormone for urine concentration and dilution. In addition, the hormone also enhances the permeability of the collecting ducts of the inner medulla to urea. After drinking large amounts of water, blood is diluted, crystal osmolarity decreases, and antidiuretic hormone secretion is reduced. Laboratory tests for decreased secretion of antidiuretic hormone (adh): 1. Plasma osmolality decreases with decreasing blood sodium; 2. Urinary osmolality increases with blood sodium <125 mmol/L along with urinary sodium >20 mmol/L and up to 80 mmol/L or more; 3. Serum chloride and BUN decrease mildly. 4, water load ADH inhibition test: drink a lot of water in a short period of time (drink 20ml/kg body weight within half an hour), normal people should urinate a lot due to the reduction of ADH release, and 80% of the amount of water drunk can be excreted within 5 hours, and the urine osmolality can be lower than 100mOsm/kg H2O (lower than plasma osmolality), while SLADH patients urinate <40% of the amount of water drunk, and the urine osmolality > plasma osmolality. This test is risky and should be performed selectively (blood sodium > 125 mmol/L without significant symptoms). (1) Principle: In the case of hypertonic urine, the water loading test can be used to identify the normal human water loading can inhibit pituitary AVP release. This test is generally done when the blood sodium is > 125 mmol/L, otherwise there is a risk of inducing water intoxication. When the blood sodium is lower than 125mmol/L, water restriction can first make the blood sodium rise before doing. (2) Method: Empty the bladder of the patient at 6:00 am, leave the first urine specimen until 7:30 am, measure the urine volume and urine osmolality, and give 1L of water (or 20ml/kg) at the same time. Drink within 10-20 min, lie flat for 5 h, and retain urine once at 8:30, 9:30, 10:30, and 11:30, for a total of 5 times. Blood was drawn at 7:00, 8:00, 9:00, 10:00, and 11:00 for plasma osmolality examination during the interval between urination. (3) Judgment of results: Normal people have diuretic effect during water loading, 80% of water is excreted within 5h, and urine osmolality is reduced to 100mOsm/kgH2O (specific gravity is about 1,003), which is lower than plasma osmolality. In contrast, the urine volume of patients with this disease is less than 40% of the water intake, and they cannot excrete hypotonic urine, and the urine osmolality > plasma osmolality. Occasionally, the urine osmolality of patients with SIAVP can be lower than plasma osmolality after strict sodium restriction, but the urine osmolality still cannot be reduced to the ideal level (still greater than 100mOsm/kgH2O).