At a Glance
Why Get Tested?
To detect a problem with the body's electrolyte balance.
When to Get Tested?
As part of routine blood testing, or when your doctor suspects that you have an imbalance of one of the electrolytes (usually sodium or potassium), or if your doctor suspects an acid-base imbalance. Electrolytes may also be checked if you are prescribed certain drugs, particularly diuretics or ACE inhibitors.
A blood sample taken from a vein in the arm
Test Preparation Needed?
The Test Sample
What is being tested?
Electrolytes are minerals that are found in body tissues and blood in the form of dissolved salts. As electrically charged particles, electrolytes help move nutrients into and wastes out of the body's cells, maintain a healthy water balance, and help stabilise the body's acid/base (pH) level. Electrolytes are usually measured as part of a renal profile which measures the main electrolytes in the body, sodium (Na+), potassium (K+), together with creatinine and/or urea, and may occasionally include chloride (Cl-) and/or bicarbonate (HCO3-).
Most of the body's sodium is found in the extracellular fluid (ECF), outside of the body’s cells, where it helps to regulate the amount of water in your body. Potassium is found mainly 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 as small changes in the plasma K+ concentration 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, which is excreted and reabsorbed by the kidneys, is to help maintain a stable pH level and, secondarily, to help maintain electrical neutrality.
Your diet provides sodium, potassium, and chloride; your kidneys excrete them. Your lungs provide oxygen and regulate CO2 which is in balance with the bicarbonate level in plasma. 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.
A related "test" is the anion gap, which is actually a calculated value. It reflects the difference between the positively charged ions (called cations) and the negatively charged ions (called anions). There is more than one formula: one is sodium minus (chloride plus bicarbonate) and the other is (sodium plus potassium) minus (chloride plus bicarbonate). 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 suggest certain kinds of metabolic abnormalities, such as starvation or diabetes, or the presence of a toxic substance, such as oxalate, glycolate, or aspirin.
How is the sample collected for testing?
A blood sample is taken 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.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.