• Dr Stella E. Okereke-Nwokeji

Understanding serum electrolytes

The electrolyte panel is used to identify an electrolyte, fluid, or pH imbalance (acidosis or alkalosis). It is frequently ordered as part of a routine physical. It may be ordered by itself or as a component of a basic metabolic panel (BMP) or a comprehensive metabolic panel (CMP). These panels can include other tests such as BUNcreatinine, and glucose.

Electrolyte measurements may be used to help investigate conditions that cause electrolyte imbalances such as dehydrationkidney diseaselung diseases, or heart conditions. Repeat testing may then also be used to monitor treatment of the condition causing the imbalance.

Since electrolyte and acid-base imbalances can be present with a wide variety of acute and chronic illnesses, the electrolyte panel is frequently used to evaluate patients both in the emergency room as well as hospitalized patients.

The electrolyte panel typically includes tests for:

  • Sodium (135-145mEq/L)—most of the body's sodium is found in extracellular fluid, outside of the body's cells, where it helps to regulate the amount of water in the body.

  • Potassium (3.5-5.5mEq/L)—this electrolyte 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 potassium level can affect the heart's rhythm and ability to contract.

  • Chloride(95-105mEq/L) —this electrolyte moves in and out of the cells to help maintain electrical neutrality and its level usually mirrors that of sodium.

  • Bicarbonate—the main job of bicarbonate (or total CO2, an estimate of bicarbonate), which is released and reabsorbed by the kidneys, is to help maintain a stable pH level (acid-base balance) and, secondarily, to help maintain electrical neutrality.

  • Other values include Calcium: 8.5-10.9mEq/L; Magnesium: 1.5-.5mEq/L; Phosphorus: 5-4.5mEq/L

The results for an electrolyte panel may also include a calculation for anion gap (see Common Questions #1).

If a person has an imbalance of a single electrolyte, such as sodium or potassium, the health practitioner may order repeat testing of that individual electrolyte, monitoring the imbalance until it resolves. If someone has an acid-base imbalance, the health practitioner may also order tests for blood gases, 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.

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When is it ordered?

An electrolyte panel may be ordered as part of a routine screening or as a diagnostic aid when a person has signs and symptoms, such as: 

  • Fluid accumulation (edema)

  • Nausea or vomiting

  • Weakness

  • Confusion

  • Irregular heart beat (cardiac arrhythmias)

It is frequently ordered as part of an evaluation when someone has an acute or chronic illness and at regular intervals when a person has a disease or condition or is taking a medication that can cause an electrolyte imbalance. Electrolyte tests are commonly ordered at regular intervals to monitor treatment of certain conditions, including high blood pressure (hypertension), heart failurelung diseases, and liver and kidney disease.

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What does the test result mean?

High or low electrolyte levels can be caused by several conditions and diseases. Generally, they are affected by how much is consumed in the diet and absorbed by the body, the amount of water in a person's body, and the amount eliminated by the kidneys. They are also affected by some hormones such as aldosterone, a hormone that conserves sodium and promotes the elimination of potassium, and natriuretic peptides, which increase elimination of sodium by the kidneys.

With respect to the amount of water in a person's body, people whose kidneys are not functioning properly, for example, may retain excess fluid. This results in a dilution effect on sodium and chloride so that they fall below normal concentrations. On the other hand, people who experience severe fluid loss may show an increase in potassium, sodium, and chloride concentrations. Some conditions such as heart disease and diabetes may also affect the fluid and electrolytes balance in the body and cause abnormal levels of electrolytes.

Knowing which electrolytes are out of balance can help a health practitioner determine the underlying cause and make decisions about treatment to restore proper balance. Left untreated, an electrolyte imbalance can lead to various problems, including dizziness, cramps, irregular heartbeat, and possibly death.

See the individual test articles on the components of the electrolytes panel for additional information on what results might mean:

  • Sodium (see reference range)

  • Potassium (see reference range)

  • Chloride (see reference range)

  • Bicarbonate (see reference range)

Is there anything else I should know?

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. Taking substantially more than the recommended dosage of antacids can also cause low chloride levels.

Some drugs may increase bicarbonate (total CO2) levels. These include, among others, fludrocortisone, barbiturates, hydrocortisone, loop diuretics, and steroids. 

Drugs that may decrease bicarbonate (total CO2) levels include methicillin, nitrofurantoin, tetracycline, thiazide diuretics, and triamterene.

Some diuretics, which may be used for people with disorders such as high blood pressure or kidney disease, tend to lower potassium levels to dangerously low levels. To avoid this problem, a health practitioner may prescribe a potassium-sparing diuretic.

A non-physiological cause of a high potassium level in a patient sample is leakage from the blood cells if the sample is not handled carefully or is delayed in transport to the lab. If a significant amount of potassium leaks from cells, it can contribute to a falsely high test result. When a healthcare provider suspects that a potassium result is not consistent with a patient's condition, the test for potassium may be repeated.