Sodium (Na) in Blood

Blood Sodium

Test Overview

A sodium test checks how much sodium (an electrolyte and a mineral) is in the blood. Sodium is both an electrolyte and mineral. It helps keep the water (the amount of fluid inside and outside the body's cells) and electrolyte balance of the body. Sodium is also important in how nerves and muscles work.

Most of the sodium in the body (about 85%) is found in blood and lymph fluid. Sodium levels in the body are partly controlled by a hormone called aldosterone, which is made by the adrenal glands. Aldosterone levels tell the kidneys when to hold sodium in the body instead of passing it in the urine. (See an illustration of the adrenal glands or the kidneys.) Small amounts of sodium are also lost through the skin when you sweat.

Most foods have sodium naturally in them or as an ingredient in cooking. Sodium is found in table salt as sodium chloride or in baking soda as sodium bicarbonate. Many medicines and other products also have sodium in them, including laxatives, ASA, mouthwash, and toothpaste.

Too much sodium in the diet may raise blood pressure in some people. For those who have high blood pressure, eating foods with a lot of sodium makes their chance of heart disease, stroke, and kidney damage higher. Heart failure gets worse when too much sodium is eaten. It increases the amount of water the body holds in and this causes swelling of the legs and hands. Some people have problems when they eat more than 4,000 milligrams (mg) of sodium per day.

Low sodium levels are uncommon and most often occur as a side effect of taking medicines that make you urinate more, such as diuretics. Severe diarrhea or vomiting or heavy sweating may also cause low sodium levels.

Other electrolytes, such as potassium, calcium, chloride, magnesium, and phosphate, may be checked in a blood sample at the same time as a blood test for sodium.

	Go to top of page	Go to next section
Author:	Jan Nissl, RN, BS	Last Updated: January 10, 2007
Medical Review:	Martin Gabica, MD - Family Medicine Avery L. Seifert, MD - Urology Andrew Swan, MD, CCFP, FCFP - Family Medicine
© 1995-2008 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.