Causes of Hyponatremia

Hyponatremia is caused by conditions such as water retention and renal failure that result in a low sodium level in the blood.

Pseudohyponatremia occurs when too much water is drawn into the blood; it is commonly seen in people with hypoglycemia (low blood sugar).

Psychogenic polydipsia occurs in people who compulsively drink more than four gallons of water a day.

Hypovolemic hyponatremia (with low blood volume due to fluid loss) occurs in dehydrated people who rehydrate (drink a lot of water) too quickly, in patients taking thiazide diuretics, and after severe vomiting or diarrhea.

Hypervolemic hyponatremia (high blood volume due to fluid retention) occurs in people with liver cirrhosis, heart disease, or nephrotic syndrome. Edema (swelling) often develops with fluid retention.

Euvolemic hyponatremia (decrease in total body water) occurs in people with hypothyroidism, adrenal gland disorder, and disorders that increase the release of the antidiuretic hormone (ADH), such as tuberculosis, pneumonia, and brain trauma.

Signs and Symptoms of Hyponatremia

Symptoms of hyponatremia are related to the severity and the rate at which the conditions develop. The first symptoms are fatigue, weakness, nausea, and headache. More severe cases cause confusion, seizure, coma, and death.

Treatment The goal of treatment is to restore electrolyte balance for proper hydration and use of total body fluid. Sodium deficiency must be corrected slowly because drastic change in sodium level can cause brain cell shrinkage and central pontine myelinolysis (damage to the pons region of the brain). Methods include:

  • Fluid and water restriction
  • Intravenous (IV) saline solution of 3% sodium
  • Salt tablets

Conivaptan (Vaprisol) has been approved by the U.S. Food and Drug Administration (FDA) to treat hypervolemic hyponatremia and euvolemic hyponatremia in some hospitalized adults. Vaprisol is administered intravenously (i.e., into a vein). Blood sodium levels should be closely monitored in patients who receive this medication. Side effects include injection site reactions, headache, thirst, and low potassium levels.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 30 Apr 2001

Last Modified: 14 Sep 2015