Hypernatremia

Hypernatremia or hypernatraemia is an elevated sodium level in the blood, specifically a serum level above 145 mEq/L. Hypernatremia is generally not caused by an excess of sodium, but rather by a relative deficit of free water in the body. For this reason, hypernatremia often coincides with dehydration.

Water is lost from the body in a variety of ways, including perspiration, imperceptible losses from breathing, and in the feces and urine. If the amount of water ingested consistently falls below the amount of water lost, the plasma sodium level will begin to rise, leading to hypernatremia. Rarely, hypernatremia can result from massive salt ingestion, such as may occur from drinking seawater or excessive amounts of a salty liquid like soy sauce. When the total protein concentration is low in serum, a falsely high sodium measurement (pseudohypernatremia) tends to occur with the usual assay method, indirect potentiometry, an artifact explained by the electrolyte exclusion effect.