Sodium is one of the most important minerals in the body. It is also an electrolyte, which means it carries an electrical charge when it is dissolved in blood. Sodium helps regulate the water balance (the amount of fluid inside and surrounding the cells) and electrolyte balance of the body. Sodium also plays an important role in nerve and muscle functions.

Most of the sodium in the body (about 85%) is found in the fluids that surround the body's cells (such as blood and lymph fluid). Sodium levels in the body are partially controlled by a hormone called aldosterone, which is produced by the adrenal glands. Aldosterone causes the kidneys to retain sodium that is normally lost through the urine. Small amounts of sodium are also lost through the skin in sweat.

Almost all foods contain sodium naturally or as an ingredient, such as table salt (sodium chloride) or baking soda (sodium bicarbonate) added during processing or cooking. Many medicines and other products also contain sodium, including laxatives, aspirin, mouthwash, and toothpaste.

Too much sodium in the diet may raise blood pressure in some people. For those who already have high blood pressure, a diet high in sodium may further increase their risk of heart disease, stroke, and kidney damage. High sodium levels can worsen congestive heart failure (CHF) and can increase the amount of water retained by the body, leading to swelling of the legs and hands. Taking in more than 4 grams (g) of sodium per day causes problems for some people.

Low blood sodium levels are uncommon and most often occur as a side effect of taking drugs that increase urination (diuretics). Severe diarrhea or vomiting or heavy sweating may also cause low blood sodium levels.

This test is usually done on a blood sample taken from a vein. Sodium can also be measured in a urine sample.

Sodium (Na)
Results

Normal

Normal values may vary widely from lab to lab.

The doctor will consider several factors when interpreting urine sodium levels, including dietary intake of sodium, the body's water content, blood sodium level, underlying disease, and medication use. For example, a high level of sodium in the urine may be caused by a high intake of salt in the diet.

Greater than normal values may mean

• High blood sodium levels (hypernatremia) can be caused by having a high-sodium diet or not drinking enough water (dehydration).
• High blood sodium levels can also result from abnormally high levels of the hormone aldosterone (hyperaldosteronism) or from dehydration caused by severe vomiting or diarrhea, Cushing's syndrome, kidney disease or injury, or a condition caused by the inability to regulate levels of water in the body properly (diabetes insipidus).

Lower than normal values may mean

• Low blood sodium levels (hyponatremia) can be caused by excessive sweating, severe vomiting or diarrhea, or drinking too much water (psychogenic polydipsia).
• Low blood sodium levels can also be caused by underactive adrenal glands or thyroid gland, heart failure, kidney disease, cirrhosis, cystic fibrosis, or SIADH (syndrome of inappropriate antidiuretic hormone secretion).