The term hyponatremia refers to a condition where the blood level of the electrolyte sodium is too low. A healthy sodium level is between 135 and 145 mmol/l and a person is considered to be hyponatremic if their blood sodium falls to below 135 mmol/l. The word hyponatremia is made up of two words – “hypo” meaning low and “natrium,” the Latin name for sodium.
The clinical significance of this condition depends on how severe it is, how quickly it has manifested and what the underlying cause is.
Hyponatremia may be brought on by either a deficiency of sodium or an excess of water diluting the level of sodium. However, most cases are caused by an excess of water rather than by a loss of sodium. This electrolyte helps to regulate the amount of water contained in and around the body’s cells, which maintains normal blood pressure and supports cell function. When the sodium level is low, the body’s water level rises causing the cells to swell, which can cause a number of problems that ranging from mild to severe. Swelling in the brain is particularly dangerous as the brain is confined to the skull and cannot swell without causing complications.
Mild hyponatremia – Some examples of the symptoms seen in mild cases of hyponatremia include lethargy, nausea and anorexia.
Severe hyponatremia – Severe hyponatremia can lead to problems such as disorientation, agitation, neurological deficits, seizures, edema of the brain and even coma.
Causes of hyponatremia
The three main causes of hyponatremia are an excess level of body water (hypervolemic hyponatremia); a water level that is too high (euvolemic hyponatremia) and low levels of both water and sodium (hypovolemic hyponatremia). Some examples of factors that can cause hyponatremia include severe vomiting and diarrhea, which can cause the body to lose fluid; liver disease, which can lead to fluid accumulation; and the use of diuretics, which can make the body expel more sodium than usual.
Diagnosis and treatment
Hyponatremia is diagnosed based on medical history, a physical examination and the results of blood and urine tests. Treatment is aimed at addressing the underlying cause of the condition and replenishing the blood sodium levels. If the condition is moderate and due to poor diet or drinking too much water, for example, the patient may be advised to cut back on fluids and change their diuretic intake. A more severe, acute form of the condition, however will require more aggressive treatment such as intravenous fluids or medication. If the condition is caused by adrenal gland insufficiency (Addison’s disease), hormone therapy is prescribed to restore a normal sodium level.
Reviewed by Sally Robertson, BSc