Serum Sodium

Specimen Required

3-5cc Clotted Blood or Serum

Fasting Required

Purpose of the Test

To determine if concentrations of sodium are normal, too high (hypernatraemia) or too low (hyponatraemia) as part of diagnosis and monitoring the treatment of related illnesses

When this test is required

This test is a part of the routine laboratory evaluation of most patients. It is one of the blood electrolytes, which are often requested as a group group (sodium, potassium, calcium, bicarbonate), when someone has non-specific health complaints. It is also tested when monitoring treatment involving intravenous (IV) fluids or when there is a possibility of developing dehydration. Electrolytes are also commonly used to monitor treatment of certain problems, including high blood pressure, heart failure, and liver and kidney disease.The osmolality of the blood or urine may be checked as well.

What the Test Detects

This test measures the concentration of sodium in blood or urine. Sodium is an electrolyte present in all body fluids, and is vital to normal body function including nerve and muscle function. Your body tries to keep your blood sodium within a very small concentration range; it does so by:producing hormones that can increase (such as natriuretic peptides) or decrease (such as aldosterone) sodium losses in urine producing a hormone that prevents water losses (antidiuretic hormone [ADH], sometimes called vasopressin) controlling thirst (even a 1% increase in blood sodium concentration will make you thirsty and cause you to drink water, returning your sodium towards normal.) These controls regulate the amount of water and sodium in the body and control blood pressure by keeping the amount of water available. An abnormal blood sodium concentration is usually due to some problem with one of these systems. When the concentration of sodium in the blood changes, the water content in your body changes. These changes can be associated with dehydration (too little fluid) or oedema (too much fluid, often resulting in swelling in the legs) and changes in blood pressure. In some people, too much sodium from salt in the diet can contribute to high blood pressure.

Preparation for the Test

None

Sample Requirements

A blood sample is taken by needle from the arm. In some cases, a random urine sample or a 24 hour collection may be required.

Additional Notes

Recent trauma, surgery, or shock may increase sodium concentration because blood flow to the kidneys is decreased.Drugs such as lithium and anabolic steroids may increase sodium concentration. Corticosteroids, laxatives, cough medicines and oral contraceptives may cause increased concentrations of sodium in the blood.Drugs such as diuretics, sulphonylureas (used to treat diabetes), ACE inhibitors (such as captopril), heparin, ibuprofen (NSAIDs), carbamazepine, tricyclic antidepressants, and vasopressin, among others, can decrease the sodium concentration within the blood.Check with your doctor if you have any concerns about drugs or supplements you are taking and their effect on your body.

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