The etiology of increased serum sodium is decreased body fluid volume due to dehydration. There are also diseases that cause kidney disorders such as acute and chronic glomerulonephritis. The following is an introduction to several diseases that are easily confused with this disease. 1, uremia, also known as pituitary uremia, is the lack of secretion of ADH from the posterior pituitary gland, the cause of which is unknown. Clinical characteristics of thirst, drinking, polyuria (daily urine volume of up to 5-10L), low urine relative density (1.001 a 1.005), low urine osmolality (50-200mmol / L). Clinically subdivided into idiopathic uremic and secondary uremic, the latter is due to tumors of the hypothalamic pituitary gland, brain trauma, surgery, inflammation, when the lesion involves the hypothalamic thirst center and the loss of thirst, often due to the inability to replenish the water in a timely manner, resulting in severe dehydration, or even death. When the suspicion of uremia should be peng drinking pressin test and plasma ADH measurement in order to clarify the diagnosis, if necessary, should be done to exclude pituitary tumors cranial CT and X-ray examination. 2, renal uremia for hereditary disease, clinical manifestations and uremia similar. The patients are mostly boys, the onset of several months after birth. After injection of pressin, the urine volume does not decrease, the specific gravity of urine does not increase, plasma ADH concentration is obviously increased, and can be differentiated from pituitary diabetes insipidus. 3, interstitial nephritis and renal concentrating function serious disorders Caused by a variety of etiological factors, in addition to pyelonephritis, drugs (salt, norepinephrine, etc.), low potassium, high calcium, urinary tract obstruction, gout, etc. can cause this disease. Performance of hypernatremia, polyuria, dehydration. According to the history, renal function test and serum electrolyte determination can be differential diagnosis. 4, diabetic hyperosmolar coma Mostly seen in elderly patients, before the onset of mild diabetes mellitus or even do not know have diabetes mellitus, often due to infections, the application of diuretics or glucocorticoids and other triggers. Clinical manifestations in addition to hypernatremia, dehydration, mainly for the neurological symptoms, such as confusion, drowsiness, hemiparesis, aphasia, convulsions, etc., easy to be confused with cerebrovascular accident. This disease should be differentiated from hypernatremia caused by osmotic diuretics. 5.Idiopathic hypernatremia The etiology is unknown and rare in clinic. Its diagnostic criteria are: ① persistent hypernatremia; ② no obvious dehydration and thirst; ③ urine becomes hypertonic when abstaining from drinking, indicating that the body still has the ability to secrete ADH; ④ renal tubular response to ADH, the application of pressurization can lead to water retention. It has been suggested that this disease is a syndrome of “elevated threshold” for ADH release.