Hyponatremia (Low Level of Sodium in the Blood)

Hyponatremia occurs when the body contains too little sodium Overview of Sodium's Role in the Body Sodium is one of the body's electrolytes, which are minerals that the body needs in relatively large amounts. Electrolytes carry an electric charge when dissolved in body fluids such as blood... read more for the amount of fluid it contains. The body may have too much, too little, or a normal amount of fluid. In all cases, however, sodium is diluted. For example, people with severe vomiting or diarrhea lose sodium. If they replace their fluid losses with just water, sodium is diluted.

Disorders, such as kidney disorders (for example, glomerulonephritis Glomerulonephritis Glomerulonephritis is a disorder of glomeruli (clusters of microscopic blood vessels in the kidneys with small pores through which blood is filtered). It is characterized by body tissue swelling... read more ) and other disorders (for example, cirrhosis Cirrhosis of the Liver Cirrhosis is the widespread distortion of the liver's internal structure that occurs when a large amount of normal liver tissue is permanently replaced with nonfunctioning scar tissue. The scar... read more , and heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more ), can cause the body to retain sodium and fluid. Often the body retains more fluid than sodium, which means the sodium is diluted.

Certain conditions may cause people to drink too much water (polydipsia), which can contribute to the development of hyponatremia.

Thiazide diuretics (sometimes called water pills) are a common cause of hyponatremia. These drugs increase sodium excretion, which increases water excretion. Thiazide diuretics are usually well-tolerated but can cause hyponatremia in people prone to low sodium, particularly the elderly.

The brain is particularly sensitive to changes in the sodium level in blood. Therefore, symptoms of brain dysfunction, such as sluggishness (lethargy) and confusion, occur first. If the sodium level in blood falls quickly, symptoms tend to develop rapidly and be more severe. Older people are more likely to have severe symptoms.

As hyponatremia becomes more severe, muscle twitching and seizures may occur. People may become unresponsive, aroused only by vigorous stimulation (stupor), and eventually cannot be aroused (coma). Death may follow.

Hyponatremia is diagnosed by measuring the sodium level in blood. Determining the cause is more complex. Doctors consider the person’s circumstances, including other disorders present and drugs taken. Blood and urine tests are done to evaluate the amount of fluid in the body, the concentration of blood, and content of urine.

Mild hyponatremia can be treated by restricting fluid intake to less than 1 quart (about 1 liter) per day. If a diuretic or other drug is the cause, the dose is reduced or the drug is stopped. If the cause is a disorder, it is treated.

Occasionally, people are given a sodium solution intravenously, a diuretic to increase excretion of fluid, or both, usually slowly, over several days. These treatments can correct the sodium level.

Some people, especially those with the syndrome of inappropriate secretion of antidiuretic hormone Syndrome of Inappropriate Secretion of Antidiuretic Hormone (SIADH) The syndrome of inappropriate secretion of antidiuretic hormone develops when too much antidiuretic hormone (vasopressin) is released by the pituitary gland under certain inappropriate conditions... read more , need long-term treatment for hyponatremia. Fluid restriction alone is often not enough to prevent recurrence of hyponatremia. Salt tablets can be used in people with mild to moderate chronic hyponatremia. Depending on the cause of hyponatremia and the amount of fluid in the person' body, several drugs are available for treatment.

Severe hyponatremia is an emergency. To treat it, doctors slowly increase the level of sodium in the blood with intravenous fluids and sometimes with a diuretic. Newer drugs, called vaptans, are sometimes needed. Increasing the sodium level too rapidly can result in severe and often permanent brain damage.