[hypo- + natremia]
A decreased concentration of sodium in the bloodstream, typically less than 135 mmol/L. Hyponatremia is extremely common in clinical medicine and is caused by one of the following conditions: congestive heart failure, renal failure, cirrhosis; syndrome of inappropriate antidiuretic hormone (SIADH); dehydration; thyroid or adrenal hormone dysfunction; side effects of drugs; psychogenic polydipsia; or laboratory error, i.e., pseudohyponatremia. Symptoms of hyponatremia include weakness, confusion, and anorexia. If serum sodium levels drop rapidly, seizures may occur. Treatment of hyponatremia depends on the underlying cause.
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