Also known as: Lytes
Name: Electrolyte panel
Related tests: Chloride, Potassium, Sodium
Why is the test done?
To diagnose a disturbance of fluid and electrolyte balance
When is it done?
As part of a health check, when an excess or deficiency of an electrolyte (usually sodium and potassium) is suspected, when an acid-base imbalance is suspected, or during treatment with diuretics or ACE inhibitors
What samples are required?
A blood sample taken from a vein
What is being tested?
Most sodium is found in the plasma, in the extracellular space, where it helps regulate the amount of water in the body. Potassium is found mainly inside cells. A small but important concentration of potassium is found in the plasma. Monitoring potassium is important: small changes in plasma potassium can affect the heart’s rhythm and contraction. The movement of chloride across cell membranes helps maintain electrical neutrality, and its concentrations usually mirror those of sodium. The main 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 (acid-base balance) and, secondarily, to ensure electrical neutrality.
Sodium, potassium and chloride are taken in with the diet and eliminated by the kidneys. The lungs supply oxygen and regulate the concentration of CO2, which is in balance with bicarbonate. The balance of these substances indicates that certain functions, such as heart and kidney function, are working well.
The electrolyte panel includes separate measurements of sodium, potassium, chloride and bicarbonate (or total CO2). The anion gap is a value calculated by relating the individual electrolyte measurements to one another. An abnormal value is not specific, but may suggest a metabolic abnormality, such as starvation or diabetes, or the presence of toxic substances such as oxalates, glycols or aspirin
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
If the concentration of a single electrolyte, such as sodium or potassium, is abnormal, repeated measurements of that electrolyte will be requested to monitor the imbalance until it resolves. In the case of an acid-base imbalance, blood gas analysis, which measures pH, oxygen and carbon dioxide in arterial blood, may be requested to assess the severity of the disturbance and monitor the response to treatment.
When is it requested?
The electrolyte panel may be requested as routine screening or to help with diagnosis when there are symptoms such as swelling (oedema), weakness, confusion or heart rhythm disturbances. It is often requested as part of the assessment of an acute or chronic illness and at regular intervals to monitor treatments that can disturb electrolyte balance. Electrolytes are commonly used to monitor the treatment of conditions such as high blood pressure, heart failure, and liver and kidney disease.
What does the test result mean?
Electrolyte concentrations depend on diet, the amount of water in the body and excretion by the kidneys. They are also affected by aldosterone, a hormone that promotes reabsorption of sodium and excretion of potassium, and by natriuretic peptides, which promote excretion of sodium by the kidneys.
In specific disorders, the concentrations of one or more electrolytes may be abnormal. However, particular attention is paid to sodium and potassium concentrations. In impaired kidney function, for example, water is retained and sodium and chloride are diluted, lowering their concentrations. In severe fluid loss, potassium, sodium and chloride concentrations rise. Electrolyte disturbances also occur in some heart, muscle and nerve diseases and in diabetes.
Identifying which electrolyte is abnormal makes it possible to find the cause and restore the balance with appropriate treatment. If untreated, an electrolyte imbalance can cause dizziness, cramps, heart rhythm disturbances and even death.
Is there anything else I should know?
Depending on the electrolyte and the extent of the imbalance, treatment may involve changing the amount of salt in the diet, increasing fluids to dilute the electrolyte concentration, or taking diuretics. Once treatment has started, the test must be repeated to check its effectiveness and prevent relapse.
Falsely high potassium concentrations can be due to errors in collecting or handling the sample. In this case the blood test must be repeated to check the result.
Some medicines, such as anabolic steroids, corticosteroids, laxatives, cough medicines and oral contraceptives, can raise sodium concentrations. Other medicines, such as diuretics, carbamazepine and tricyclic antidepressants, can lower them.
Medicines that change sodium concentrations can also cause changes in chloride. In addition, taking large doses of sodium bicarbonate or antacids, above the prescribed dose, can lower chloride concentrations.
Some medicines can raise bicarbonate (total CO2) levels, such as fludrocortisone, barbiturates, bicarbonate, hydrocortisone, loop diuretics and steroids. Medicines that lower bicarbonate (total CO2) levels include methicillin, nitrofurantoin, tetracyclines, thiazide diuretics and triamterene
What is the anion gap?
Specifically, the anion gap assesses the difference between measured and unmeasured ions or electrolytes in the blood. According to the principle of electrical neutrality, the number of positive ions (cations) and negative ions (anions) must be equal. However, not all ions are measured routinely. The calculated anion gap reflects the unmeasured ions, mainly the anions, hence the name “anion gap”. The most commonly used formula is:
Anion gap (AG) = Sodium – (Chloride + Bicarbonate [total CO2])
However, there are other AG formulas, so reference ranges are not interchangeable. Each laboratory’s formula should have a defined and documented reference range
The anion gap is not specific. It is raised when the number of anions increases, indicating anion gap metabolic acidosis, but not the cause of the imbalance. Metabolic acidosis must be treated to restore the acid-base balance, but the cause must also be identified and treated. Causes can include uncontrolled diabetes, starvation, kidney damage and ingestion of potentially toxic substances such as antifreeze, excessive doses of aspirin or methanol. A low anion gap can also occur; it is seen when albumin (both an anion and a protein) is reduced, while immunoglobulins (both cations and proteins) are increased