• Hyponatremia means a low plasma sodium level
• Hypernatremia means a high plasma sodium level
• Hyponatremia typically causes neurological depression
• Hypernatremia typically causes neurological excitation
• Both hypernatremia and hypernatremia can ultimately cause fits, coma and death
• Hyponatremia can be caused by water retention or loss of both sodium and water followed with replacement mainly with water
• Hypernatremia can be caused by loss of a dilute fluid such as dilute urine or by inappropriate sodium retention in the kidney.
• Hyponatremia is treated with fluid restriction if body volume is raised and by administration of sodium and water if body volume is low
• Hypernatremia is treated by water replacement
• Both hypernatremia and hypernatremia should be corrected slowly with careful monitoring

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Primary aldosteronism
Ganguly A, 1998
N Engl J Med 339 1828-1834

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C. A. O'Callaghan 2004