Sodium blood test: normal range explained

A sodium blood test measures the amount of sodium in your blood. Sodium is an electrolyte, a mineral that carries an electric charge in body fluids; it helps control how much fluid your body holds and the balance of acids and bases, and it keeps nerves and muscles working. Your blood level is a balance between the sodium and water you take in and the amount your kidneys pass into urine, with small losses in sweat and stool.

Doctors order sodium as part of an electrolyte panel or a basic or comprehensive metabolic panel, often in a routine check-up, and on its own when they want to track sodium. MedlinePlus lists medicines that affect fluid balance, such as diuretics, and symptoms of too much or too little sodium, such as confusion, weakness or muscle twitching, as other reasons. Its encyclopedia page adds recent surgery, serious illness, IV fluids and steroid medicines.

Sodium moves with water more than with salt, so fluid loss and fluid gain both change it.

• Losing fluid through vomiting, diarrhoea, heavy sweating or burns, or drinking too little, can push sodium up; losing sodium itself through vomiting or diarrhoea can pull it down.
• Drinking a very large amount of water lowers sodium.
• Diuretics, or water pills, and other medicines such as some antidepressants, pain relievers, lithium and corticosteroids can move sodium in either direction. Do not stop a medicine unless your doctor tells you to.
• Heart failure, kidney disease and cirrhosis of the liver can lower sodium by making the body hold extra water, which your doctor considers.
• Hormone conditions, including problems with the adrenal glands, the thyroid or antidiuretic hormone, change sodium.
• Sodium runs slightly lower in pregnancy because blood volume expands.