Hypernatremia overview

Overview

Hypernatremia is an electrolyte disturbance consisting of an elevated sodium level in the blood (compare to hyponatremia, meaning a low sodium level). It is defined as a serum sodium concentration exceeding 145 mEq/L. The most common cause of hypernatremia is not an excess of sodium, but a relative deficit of free water in the body. For this reason, hypernatremia is often synonymous with the less precise term dehydration.

Pathophysiology

The main cause of hypernatremia is water loss with the inability to replace the losses either because of a defective thirst mechanism or inability to access water. Sosium retention is an uncommon cause.

Causes

As mentioned before, water loss and sodium retention are the main culprits. water loss can be due to wasting of a significant amount of free water through the excretion of dilute urine (eg, diabetes insipidus), the GI tract (diarrhea), perspiration or any hypothalamic disease that can alter the thirst response to water deficit.

Differential diagnosis

The differential diagnosis of the etiology of hypernatremia is wide but mainly involves the kidney, the hypothalamus, the skin, the endocrine system (diabetes mellitus, adrenals and thyroid diseases) and the GI tract.

Diagnosis

Diagnosis relies on a constellation of findings including:

Symptoms

Usually nonspecific with lethargy and weakness being predominant. At higher levels of sodium concentrations, seizures and neurologic dysfunction become more evident.

History

It should include any history of renal, GI or endocrine diseases. Moreover, drug and diet knowledge is essential for diagnosing the etiology.

Labs

The urine osmolarity can help differentiate renal from extrarenal causes. The water deprivation test can help define the origin of diabetes insipidus (neurogenic vs nephrogenic)

Treatment

It aims at correcting the free water deficit and removing the offending drug or osmotic agent. Specific etiologies such as DI can be treated accordingly.