Etiologies of increased serum sodium include decreased fluid volume due to dehydration. There are also diseases caused by kidney diseases such as acute and chronic glomerulonephritis. Tests for increased serum sodium: 1. Decreased fluid volume, such as dehydration. 2, renal diseases such as acute and chronic glomerulonephritis with sodium and water retention, but there can be no significant change in serum sodium in clinical tests because of concurrent water retention. 3, endocrine diseases, such as primary or secondary aldosteronism appear high sodium; Cushing’s syndrome may have mildly elevated serum sodium, or long-term use of adrenocorticotropic hormone to make the renal tubular sodium reabsorption hyperactivity, and cause high serum sodium. 4, brain injury can cause hypernatremia, due to the central disorder of osmotic pressure regulation, become traumatic uremia, urine can not be concentrated, fluid loss, increased serum sodium, increased plasma osmolality, and hypotonic urine. This condition makes it difficult to normalize serum sodium even with massive hydration. Serum sodium test Serum sodium is the concentration of sodium ions in the blood serum. Sodium ion is the most abundant cation in extracellular fluid (e.g. blood) and is important for maintaining extracellular fluid volume, regulating acid-base balance, maintaining normal osmotic pressure and cellular physiological functions, and is involved in maintaining normal neuromuscular stress. Changes in extracellular fluid sodium concentration can be caused by changes in either water or sodium content, so disorders of sodium balance are often accompanied by disturbances in water balance. The normal metabolism and balance of water and sodium is an important factor in maintaining the stability of the human body environment. Therefore, serum sodium measurement is of great clinical importance, especially for the treatment of dehydration.