Definition of Hypernatremia

Hypernatremia: Elevated blood sodium.

Sodium is the major positive ion (cation) in fluid outside of cells. The chemical notation for sodium is Na⁺ (from natrium, a synonym for sodium). When combined with chloride (Cl), the resulting substance is table salt (NaCl).

Excess sodium (such as from fast food hamburger and fries) is excreted in the urine. Too much (or too little) sodium can cause cells to malfunction, and extremes can be fatal.

The normal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or in international units, 135 - 145 millimoles/liter (mmol/L).