The Test Sample
What is being tested?
Electrolytes are electrically charged minerals that are found in body tissues and blood in the form of dissolved salts. They help move nutrients into and wastes out of the body's cells, maintain a healthy water balance, and help stabilize the body’s pH level. The electrolyte panel measures the main electrolytes in the body: sodium (Na+), potassium (K+), chloride (Cl-), and bicarbonate (HCO3-; sometimes reported as total CO2).
Most sodium is found in the plasma, outside of the body's cells, where it helps to regulate the amount of water in the body. Potassium is found primarily inside the body's cells. A small but vital amount of potassium is found in the plasma, the liquid portion of the blood. Monitoring potassium is important. Small changes in the plasma K+ level can affect the heart’s rhythm and ability to contract. Chloride travels in and out of the cells to help maintain electrical neutrality, and its level usually mirrors that of sodium. The primary role of bicarbonate (or total CO2, an estimate of bicarbonate), which is excreted and reabsorbed by the kidneys, is to help maintain a stable pH level (acid-base balance) and, secondarily, to help maintain electrical neutrality.
A person's diet provides sodium, potassium, and chloride; the kidneys excrete them. The lungs provide oxygen and regulate CO2, which is in balance with bicarbonate. The balance of these chemicals is an indication of the functional well-being of several basic body functions, including those performed by the kidneys and heart.
The electrolyte panel is composed of the individual tests for sodium, potassium, chloride, and bicarbonate (or total CO2). A related "test" is the anion gap, which is a value calculated using the results of an electrolyte panel. It reflects the difference between the positively charged ions (called cations) and the negatively charged ions (called anions). The occurrence of an abnormal anion gap reflects an unusual presence of some kind of charged particle in the blood. It is non-specific but can be affected by metabolic by-products from conditions such as starvation or diabetes or the presence of a toxic substance, such as oxalate, glycolate, or aspirin. For more information on anion gap, see Common Questions #1.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.