Electrolytes are minerals that carry an electric charge. They help regulate many of your body systems including heart rhythms, nerves, and muscles. They are also involved in helping maintain the amount of fluid and the acid-base balance in your body. The kidneys control electrolyte concentrations in the blood and the most common cause of electrolyte imbalance is kidney dysfunction. 

Electrolyte tests such as sodium and potassium are used along with other tests to assess how well your kidneys, liver and some steroids and hormones are working.

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 it used?

Electrolyte measurements are used to screen for an electrolyte or pH imbalance and to monitor the effect of treatment on a known imbalance that is affecting bodily organ function such as dehydration, kidney disease, lung diseases, or heart conditions. Since electrolytes are often abnormal in a variety of acute (short term) and chronic (long-term) illnesses, they are frequently requested in hospitalised patients. Repeat testing may also be  used to monitor treatment of the conditin causing the imbalance. If someone has an acid-base imbalance, the health practitioner may also be used to monitor treatment of the condition causing the imbalance. If someone has an acid-base imbalance, the health practitioner may also order tests for blood gases, which measure the pH, 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 requested?

It may be requested as part of routine testing or as a diagnostic aid for a specific disorder, such as oedema, nausea, or vomiting, weakness, confusion or cardiac arrhythmias. Electrolyte tests are commonly ordered at regular intervals to monitor treatment or certain condition, including high blood pressure (hypertention If one or more of the electrolytes is imbalanced, your doctor may want to monitor that individual electrolyte closely while treating the cause of the imbalance.

What does the result mean?

Electrolyte levels are affected by how much is taken in through your diet, the amount of water in your body, and the quantity of electrolytes excreted by your kidneys. They are also affected by hormones, especially aldosterone, a hormone that retains sodium in the body but increases the loss of potassium.

In specific disorders, one or more electrolytes may be abnormal. Your doctor will look at the overall balance but is likely to be 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 K+, Na+, and Cl- (Cl- tends to mirror the Na+). Some forms of heart disease, muscle and nerve problems, and diabetes may also have one or more abnormal electrolytes. Electrolyte abnormalities may also be a consequence of drug treatment.

Knowing which electrolytes are out of balance can help your doctor 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?

Certain drugs, such an 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 in chloride. Taking substantially more  than the recommended dosage of antacids can also cause low chloride levels.

Some drugs may increase bicarbonate levels. These include, among others, fludrocortisone, barbiturates, hydrocortisone, loop diuretics. and steroids. Drugs that may decrease bicarbonate (total CO2) levels include methicillin, nitrofurantoin, tetracylcine, thiazide diuretics, and triamternce.

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

Depending on which electrolyte(s) is out of balance and the extent of that change, treatment may involve changing your diet, for example to lower salt intake, increasing or reducing fluid intake, or taking or stopping medication such as diuretics. Once treatment has begun, you may be asked to have regular testing to determine how well the treatment has worked and to make sure the imbalance does not reoccur.

Common questions

• What is an anion gap?

Anion gap (AG) 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 recognised 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)

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.

More information

RCPA Manual: Electrolytes

RCPA Manual: Electrolytes faeces

RCPA Manual: Electrolytes urine