Hyponatremia

Hyponatremia (American English) or hyponatraemia (British English) is an electrolyte disturbance in which the sodium (salt) concentration in the serum is lower than normal. (Hypo = low; natraemia = sodium in blood) Sodium is the dominant extracellular cation (positive ion) and cannot freely cross the cell membrane. Its homeostasis (stability) is vital to the normal function of cells. Normal serum sodium levels are between 135 and 145 mEq/L.