Reflects increased serum sodium concentration, while the total amount of sodium in the body can be increased, normal, or decreased is important for maintaining extracellular fluid volume, regulating acid-base balance, maintaining normal osmotic pressure and cellular physiological function, and is involved in maintaining normal neuromuscular stress. Serum sodium is examined in the following ways. 1.History: excessive input of sodium chloride solution, especially when the renal function is low. 2.Clinical manifestations: increased extracellular fluid is the main cause, so tissue edema, pulmonary edema and heart failure often occur. 3.Auxiliary examination: elevated or normal blood sodium level can be found. Serum sodium refers to the concentration of sodium ions in the serum. Sodium ion is the most abundant cation in extracellular fluid (such as blood), which 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 neuro-muscular 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.