Sodium

This test measures the level of sodium in the blood. Sodium is a mineral that is vital to normal body processes, which include nerve and muscle functioning. Too much sodium, however, can increase the chances of high blood pressure. Sodium is a positively charged molecule that works with other electrolytes, such as potassium, chloride, and bicarbonate (or total CO2), to help your cells function normally and help regulate the amount of fluid in the body. For example, you lose electrolytes when you sweat, and you must replace them. Sodium is present in all body fluids but is found in the highest concentration in the blood and in the fluid outside of the body’s cells. This extracellular sodium, as well as all body water, is regulated by the kidney.

We get sodium in our diet, from table salt (sodium chloride or NaCl), and to some degree from most of the foods that we eat. Most people have an adequate intake of sodium. The body uses what it requires and the kidneys excrete the rest in the urine to maintain sodium concentration within a very narrow range. It does this by:

producing hormones that can increase (natriuretic peptides) or decrease (aldosterone) sodium losses in urine,

producing a hormone that prevents water losses (antidiuretic hormone, ADH), and

controlling thirst. (Even a 1% increase in blood sodium will make you thirsty and cause you to drink water, returning your sodium level to normal.) 

Abnormal blood sodium is usually due to some problem with one of these control systems. When the level of sodium in the blood changes, the water content in your body also changes. These changes can be associated with dehydration or edema, especially in the legs.

A blood sample is taken by needle from the arm. In some cases, a urine sample may be required.

No test preparation is needed.