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 . Electrolytes may also be checked if you are prescribed certain drugs, particularly diuretics or ACE inhibitors.
A blood sample drawn from a vein in the arm.
Repeat testing over time may be required to monitor progress.
Test preparation needed?
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+ 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 main 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 help maintain proper levels by reabsorption or by elimination into the urine. 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.
Any disease or condition that affects the amount of fluid in the body, such as dehydration, or affects the lungs, kidneys, metabolism, or breathing has the potential to cause a fluid, electrolyte, or pH imbalance (acidosis or alkalosis). Normal pH must be maintained within a narrow range of 7.35 - 7.45 and electrolytes must be in balance to ensure the proper functioning of metabolic processes and the delivery of the right amount of oxygen to tissues.
A related 'test' is the anion gap, which is actually a calculated value, it reflects the difference between the positively charged ions (cations) and the negatively charged ions (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 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 obtained by inserting a needle into a vein in the arm.