Hyponatremia
Low level of sodium in the blood is called hyponatremia. The normal level is 140 meq/lL. Hyponatremia is seen when there is loss of sodium or excess water in the body which dilutes the sodium.

• Loss of sodium as in diarrhea.
• Loss of sodium from the kidney as with diuretics.
• Excess water retention as seen in heart or kidney failure.
• SIADH (Syndrome of Inappropriate ADH (hormonal) production)

Symptoms of hyponatremia depend on the rapidity with which sodium level drops. Usually, patients present with confusion, and sometimes even seizures, coma and death if levels are too low.

Hypernatremia
Hypernatremia is characterized by increased sodium level in the blood. It is more a disorder of water metabolism and is seen when the ratio of solutes to water in the body is increased.

Causes of Hypernatremia

• Impaired thirst e.g. coma.
• Presence of osmotic substances in the urine which cause excessive water loss, e.g. glucose, mannitol administartion, diabetic ketoacidosis.
• Excess loss of water from the kidney as in diabetes insipidus.
• Excess loss of water from the skin: e.g. sweating, burns.