Hypernatremia is a disturbance of the physical electrolyte balance. Hypernatremia is accompanied by an increased concentration of sodium in the blood. The normal concentration of sodium in the blood is between 135 and 145 millimoles per liter (moles are used to indicate the amount of sodium in chemical reactions).

If the level is increased to a value of more than 145 millimoles per liter, this is called hypernatremia. Normally, even slightly increased sodium concentrations trigger a feeling of thirst in our body. In most cases, the hypernatremia is compensated relatively quickly by the intake of fluid.


The most common cause of an increased sodium content in our blood is a so-called hypovolemic hypernatremia. In this case the sodium concentration increases due to fluid loss. The body therefore loses too much water.

Known causes are permanent diarrhoea, vomiting, heavy sweating or medication such as dehydration tablets. A special form of diabetes, the so-called diabetes insipidus, also leads to hypernatremia through extremely high fluid loss. This is caused by a defective regulation in the brain or kidney.

The body loses the ability to withdraw water from the primary or fore urine produced in the kidney. Consequently, the body excretes enormous amounts of urine, between 5 and 25 liters per day. If too little fluid is supplied to the body from outside, this also ends in dehydration with hypernatremia.

This mainly affects older people who often forget to drink because of their reduced thirst. The opposite of hypovolemic hypernatremia is hypervolemic hypernatremia. This can be triggered, for example, by drinking salty seawater or as part of a medical infusion therapy with saline solution.

Another possible cause is the so-called Conn syndrome, a disease of the adrenal cortex that leads to hypernatremia. The adrenal gland produces too much aldosterone, which causes the kidney to withdraw sodium from the primary or forebrain. This dysregulation thus restricts the excretion of sodium and leads to hypernatremia.