Most sodium is found in the plasma, outside of the body’s cells, where it helps to regulate the amount of water in your 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 exreted and reabsorbed by the kidneys, is to help maintain a stable pH level (acid-base balance) 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 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 carbon dioxide). A related "test" is the anion gap, which is actually a value calculated using the results of an electrolyte panel. 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. For more information on anion gap, click here.
How is the sample collected for testing?A blood sample is drawn by needle from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?No test preparation is needed.
How is it used?The electrolyte panel is frequently ordered as part of a routine physical, either by itself or as components of a basic metabolic panel or comprehensive metabolic panel. It is used to screen for an electrolyte or acid-base imbalance and to monitor the effect of treatment on a known imbalance that is affecting bodily organ function. Since electrolyte and acid-base imbalances can be present with a wide variety of acute and chronic illnesses, the electrolyte panel is frequently ordered for hospitalized patients and those who come to the emergency room.
If a patient has a single electrolyte that is high or low, such as sodium or potassium, the doctor may order repeat testing of that individual electrolyte, monitoring the imbalance until it resolves. If a patient has an acid-base imbalance, the doctor may order blood gas tests, which measure the pH and oxygen and carbon dioxide levels in an arterial blood sample, to help evaluate the severity of the imbalance and monitor its response to treatment.
When is it ordered?It may be ordered as part of a routine screening or as a diagnostic aid when a patient has symptoms, such as edema, nausea, weakness, confusion, or cardiac arrhythmias. It is frequently ordered as part of an evaluation when a patient has an acute or chronic illness and at regular intervals when a patient has a disease or condition or is taking a medication that can cause an electrolyte imbalance. Electrolytes are commonly used to monitor treatment of certain problems, including high blood pressure (hypertension), heart failure, and liver and kidney disease.
What does the test result mean?Electrolyte levels are affected by how much is taken in through your diet, the amount of water in your body, and the amount of electrolytes excreted by your kidneys. They are also affected by compounds such as aldosterone, a hormone that conserves sodium and increases the loss of potassium, and natriuretic peptides, which increase renal losses of sodium.
In specific disorders, one or more electrolytes may be in an abnormal concentration. Your doctor will look at the overall balance but is especially concerned with your sodium and potassium levels. People whose kidneys are not functioning properly, for example, may retain excess fluid in the body, diluting the sodium and chloride so that they fall below normal concentrations. Those who experience severe fluid loss may show an increase in potassium, sodium, and chloride. Some forms of heart disease, muscle and nerve problems, and diabetes may also have one or more abnormal electrolytes.
Knowing which electrolytes are out of balance can help your doctor to determine the cause and treatment to restore proper balance. If left untreated, electrolyte imbalance can lead to dizziness, cramps, irregular heartbeat, and possibly death.
Is there anything else I should know?Depending on which electrolyte(s) is out of balance and the extent of that change, treatment may involve changing your diet to lower salt intake, increasing fluids to dilute the electrolyte concentration, taking diuretics, and medicating the imbalance. Once a treatment has begun, you may be asked to get regular testing to determine how well the treatment worked and to make sure the imbalance does not reoccur.
Potassium levels can be falsely elevated by several different specimen-collection or –processing errors. If there are any questions as to how your blood was collected, your doctor may request that the test be repeated to verify results.
Certain drugs such as anabolic steroids, corticosteroids, laxatives, cough medicines, and oral contraceptives may cause increased levels of sodium. Other drugs such as diuretics, carbamazepine, and tricyclic antidepressants may cause decreased levels of sodium.
Drugs that affect sodium blood levels will also cause changes in chloride. In addition, swallowing large amounts of baking soda or substantially more than the recommended dosage of antacids can also cause low chloride.
Some drugs may increase bicarbonate (total CO2) levels including: fludrocortisone, barbiturates, bicarbonates, hydrocortisone, loop diuretics, and steroids. Drugs that may decrease bicarbonate (total CO2) levels include methicillin, nitrofurantoin, tetracycline, thiazide diuretics, and triamterene.
What is anion gap?Anion gap (AG or AGAP) is a value calculated using the results of an electrolyte panel. It is used to help distinguish between anion-gap and non-anion-gap metabolic acidosis. Acidosis refers to an excess of acid in the body; this can disturb many cell functions and should be recognized as quickly as possible, when present. AG is frequently used in the hospital and/or emergency room setting to help diagnose and monitor acutely ill patients. If anion-gap metabolic acidosis is identified, the AG may be used to help monitor the effectiveness of treatment and the underlying condition.
Specifically, the anion gap evaluates the difference between measured and unmeasured electrical particles (ions or electrolytes) in the fluid portion of the blood. According to the principle of electrical neutrality, the number of positive ions (cations) and negative ions (anions) should be equal. However, not all ions are routinely measured. The calculated AG result represents the unmeasured ions and primarily consists of 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 formula will have an established normal range that should be referenced.
The anion gap is non-specific. It is increased when the number of unmeasured anions increases, indicating a state of anion-gap metabolic acidosis, but it does not tell the doctor what is causing the imbalance. The metabolic acidosis must be treated to restore the acid/base balance, but the underlying condition must also be identified and treated. Causes can include uncontrolled diabetes, starvation, kidney damage, and ingestion of potentially toxic substances such as antifreeze, excessive amounts of aspirin, or methanol. A low anion gap can also occur; this is most commonly seen when albumin (an anion as well as a protein) is low, while immunoglobulins (cations as well as proteins) are increased.