Blood Sodium Level
Blood Sodium Level
Sodium is a mineral that is found throughout the body and is crucial (along with other electrolytes) to the appropriate balance of fluid in the body. Sodium is primarily found in bodily fluids and blood. For the body to function normally, blood sodium levels have to be maintained at a very narrow range; when sodium levels are too high or too low, serious health consequences can result. The body keeps its sodium levels in equilibrium by prompting the kidneys to resorb more (when the body needs sodium) or excrete more (when there is excess sodium). The hormones responsible for stimulating the processing of sodium in the kidneys are called natriuretic peptides, which prompt the kidneys to excrete sodium into the urine and out of the body; aldosterone, which prompts the kidneys to hold onto or resorb sodium; and antidiruetic hormone or ADH, which prompts the retention of fluids in the bloodstream, thus increasing the amount of water in the bloodstream and diluting the blood sodium level. The mechanism of thirst is another important way that blood sodium levels are controlled; as small as a 1% increase in blood sodium level will prompt thirst, which initiates drinking behavior and serves to drop the elevated blood sodium level. When blood sodium levels get too high, the condition is called hypernatremia. When blood sodium levels get too low, the condition is called hyperkalemia.
A blood sodium level is usually drawn as part of a larger panel of electrolytes. Other measurements in the electrolyte panel include chloride, potassium, and carbon dioxide. A blood sodium level is usually checked during a routine physical examination, as well as when there are concerns about the functioning of the patient’s kidneys; when the patient has high blood pressure (hypertension); to monitor sodium levels during the use of intravenous fluid therapy; in patients on dialysis; in patients who have symptoms of heart failure or who are known to have heart failure; in patients with liver disease; in patients with lower leg swelling or other fluid accumulation; and in patients with symptoms that could possibly be due to electrolyte imbalance, specifically low blood sodium levels or hyponatremia. These symptoms can include confusion, severe fatigue and weakness, extreme thirst, low urine output, muscle twitching, irritability, or agitation.
Blood sodium levels can be affected by a number of medications. Patients who are on these medications should inform their doctor, so that test results can be interpreted appropriately. Medications that increase blood sodium levels include birth control pills, some antibiotics, clonidine, steroid medications, anabolic steroid use, cough preparations, laxatives, methyldopa, and nonsteroidal anti-inflammatory agents (including ibuprofen). Medications that decrease blood sodium levels include carbamazepine, diuretics, sulfonylureas, triamterene, and vasopressin. Other factors that may skew the results of blood sodium level include intravenous infusion of fluids containing sodium; excess ingestion of food or beverages containing salt; excess consumption of fluids; use of the hormone aldosterone; and recent severe injury, surgery, or shock.
Patients who are taking anticoagulant medications should inform their healthcare practitioner since this may increase their chance of bleeding or bruising after a blood test.
This test requires blood to be drawn from a vein (usually one in the forearm), generally by a nurse or phlebotomist (an individual who has been trained to draw blood). A tourniquet is applied to the arm above the area where the needle stick will be performed. The site of the needle stick is cleaned with antiseptic and the needle is inserted. The blood is collected in vacuum tubes. After collection, the needle is withdrawn and pressure is kept on the blood draw site to stop any bleeding and decrease bruising. A bandage is then applied.
There are no restrictions on diet or physical activity, either before or after the blood test.
As with any blood tests, discomfort, bruising, and/or a very small amount of bleeding is common at the puncture site. Immediately after the needle is withdrawn, it is helpful to put pressure on the puncture site until the bleeding has stopped. This decreases the chance of significant bruising. Warm packs may relieve minor discomfort. Some individuals may feel briefly woozy after a blood test, and they should be encouraged to lie down and rest until they feel better.
Addison’s disease— A condition in which the adrenal glands are not functioning properly. Addison’s disease can be caused by a problem in the adrenal glands themselves, or in the pituitary gland, which secretes a hormone that affects the adrenal glands.
Aldosterone— A hormone secreted by the adrenal glands that prompts the kidneys to hold onto sodium.
Antidiuretic hormone (ADH)— Also called vasopressin. A hormone produced by the hypothalamus and stored in and excreted by the pituitary gland. ADH acts on the kidneys to reduce the flow of urine, increasing total body fluid.
Cushing’s syndrome— A disorder affecting the adrenal glands and their secretion of coritsol.
Diuretic— A medication that increases the flow of urine through the kidneys and out of the body.
Hypernatremia— Elevated blood sodium levels.
Hyponatremia— Low blood sodium levels.
Natriuretic peptides— Peptides that prompt the kidneys to excrete sodium into the urine and out of the body.
Basic blood tests, such as blood sodium levels, do not carry any significant risks other than slight bruising and the chance of brief dizziness.
A normal blood sodium level is 136-145 millie-quivalents per liter (mEq/L), or 136-145 millimoles per liter (mmol/L).
High blood sodium levels may be due to:
- dehydration (increased loss of body water without sufficient replacement by drinking, which often occurs in febrile illnesses, with severe diarrhea and/or vomiting, or in situations involving heavy exercise in hot weather, resulting in fluid loss through sweating);
- high blood levels of the hormone aldosterone, termed hyperaldosteronism;
- Cushing’s syndrome;
- diabetes insipidus (caused by a shortage of antidiu-retic hormone);
- diabetic keoacidosis;
- diuretic use;
- head injury or brain surgery, particularly if the pituitary gland is affected;
- sickle cell anemia;
- kidney disease;
- medications including lithium, demeclocycline, or diuretics; or
- ingestion of an extremely high-sodium diet.
Low blood sodium levels may be due to:
- Addison’s disease;
- thyroid insufficiency;
- severe diarrhea;
- diuretic use;
- excess sweating;
- serious burns;
- kidney disease, including those resulting in the loss of protein from the body (nephrotic syndrome);
- cirrhosis of the liver;
- cystic fibrosis;
- increased retention of water in the body, due to excess consumption of water, heart failure, or cirrhosis of the liver
- poor nutritional status due to alcoholism, eating disorder, other causes of malnutrition;
- disorders involving the pituitary gland;
- medications such as chlorpropamide, carbamazepine, vincristine, clofibrate, antipsychotic medications, aspirin, ibuprofen, synthetic vasopressin, and oxytocin;
- too much antidiuretic hormone (also called vasopressin) in the blood (referred to as syndrome of inappropriate antidiuretic hormone or SIADH). This syndrome can occur due to a wide variety of conditions involving the lung and brain, including brain injury, infections such as meningitis and encephalitis, pneumonia, acute respiratory failure, brain tumors, lung cancer, and psychosis;
- a number of conditions can also stimulate release of ADH from the pituitary, such as pain, stress, exercise, dehydration, increased levels of other blood electrolytes, and low blood sugar levels; or
- poor dietary intake of sodium (this is extremely rare).
Goldman L., D. Ausiello, eds. Cecil Textbook of Internal Medicine, 23rd ed. Philadelphia: Saunders, 2007.
McPherson R. A., and M. R. Pincus, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods, 21st ed. Philadelphia: Saunders, 2006.
Medical Encyclopedia. Medline Plus. U.S. National Library of Medicine and the National Institutes of Health. January 2, 2008. http://www.nlm.nih.gov/medlineplus/encyclopedia.html (February 10, 2008).
American Association for Clinical Chemistry, 1850 K Street, NW, Suite 625, Washington, DC, 20006, (800) 892-1400, http://www.aacc.org.
Rosalyn Carson-DeWitt, MD
Blood sugar test seeGlucose tests
Blood thinners seeAnticoagulant and anti-platelet drugs
Blood transfusion seeTransfusion