Also Known As
Anion Gap
Formal Name
Electrolyte Panel
This article was last reviewed on
This article waslast modified on
January 15, 2018.

Information on the Anion Gap can be found below under Common Questions.

At a Glance
Why Get Tested?

To detect a problem with the body's electrolyte balance

When To Get Tested?

As part of routine health screening or when your healthcare provider suspects that you have an imbalance of one of the electrolytes (usually sodium or potassium) or an acid-base imbalance

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

Sodium Reference Range

The reference ranges1 provided here represent a theoretical guideline that should not be used to interpret your test results. Some variation is likely between these numbers and the reference range reported by the lab that ran your test. Please consult your healthcare provider. 

Age Conventional Units2 SI Units3
0-18 years Not available due to wide variability. See child's lab report for reference range.
Adult 136-145 mEq/L 136-145 mmol/L
>90 years 132-146 mEq/L 132-146 mmol/L


Potassium Reference Range
Age Conventional Units2 SI Units3
0-18 years Not available due to wide variability. See child's lab report for reference range.
Adult 3.5-5.1 mEq/L 3.5-5.1 mmol/L


Choride Reference Range
Age Conventional Units2 SI Units3
0-18 years Not available due to wide variability. See child's lab report for reference range.
Adult 98-107 mEq/L 98-107 mmol/L
>90 years 98-111 mEq/L 98-111 mmol/L


CO2 Reference Range
Age Conventional Units2 SI Units3
0-18 years Not available due to wide variability. See child's lab report for reference range.
Adult 23-29 mEq/L 23-29 mmol/L
>60 years 23-31 mEq/L 23-31 mmol/L
>90 years 20-29 mEq/L 20-29 mmol/L

1 from Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. 5th edition, St. Louis: Elsevier Saunders; 2011.

2 Conventional Units are typically used for reporting results in U.S. labs

3 SI Units are used to report lab results outside of the U.S.

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 stabilize the body's acid/base (pH) level.

The electrolyte panel measures the blood levels of the main electrolytes in the body: sodium (Na+), potassium (K+), chloride (Cl-), and bicarbonate (HCO3-; sometimes reported as total CO2).

A person's diet provides sodium, potassium, and chloride. The kidneys help maintain proper levels by reabsorption or by elimination into the urine. The lungs provide oxygen and regulate CO2. The CO2 is produced by the body and is in balance with bicarbonate. The overall balance of these chemicals is an indication of the functional well-being of several basic body functions. They are important in maintaining a wide range of body functions, including cardiac and skeletal muscle contraction and nerve impulse conduction.

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. (For more on this, see the condition article on Acidosis and Alkalosis and also on Dehydration.)

A related "test" is the anion gap, which is a value calculated using the results of an electrolyte panel. It reflects the difference between the positively charged ions (called cations) and the negatively charged ions (called anions). An abnormal anion gap is non-specific but can suggest certain kinds of metabolic or respiratory disorders or the presence of toxic substances. For more information on anion gap, see Common Questions #1.

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.

Accordion Title
Common Questions
  • How is it used?

    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 BUN, creatinine, and glucose.

    Electrolyte measurements may be used to help investigate conditions that cause electrolyte imbalances such as dehydration, kidney disease, lung 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—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—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—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.

    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.

  • 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 failure, lung diseases, and liver and kidney disease.

  • 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:

  • 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.

  • 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. The anion gap 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 health practitioner 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 (salicylates), 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.

  • What is the treatment for an electrolyte imbalance?

    Treatment depends on which electrolyte(s) is out of balance and the extent of that change. Treatment usually involves managing the imbalance while identifying and addressing the underlying cause(s) of the imbalance and providing whatever support is necessary to the affected person.

View Sources

Sources Used in Current Review

Ambalavanan, N. (2014 February 28, Updated). Fluid, Electrolyte, and Nutrition Management of the Newborn. Medscape Drugs & Diseases [On-line information]. Available online at Accessed October 2015.

Genzen, J. and Lehman, C. (2015 April, Updated). Electrolyte Abnormalities, Life Threatening. ARUP Consult [On-line information]. Available online at Accessed October 2015.

Byrd, R. and Roy, T. (2015 July 31, Updated). Respiratory Acidosis. Medscape Drugs & Diseases [On-line information]. Available online at Accessed October 2015.

Dugdale, D. (2013 August 3, Updated). Electrolytes. MedlinePlus Medical Encyclopedia [On-line information]. Available online at Accessed October 2015.

Wisse, B. (2013 November 7, Updated). Alkalosis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at Accessed October 2015.

Dugdale, D. (2013 October 29, Updated). Metabolic acidosis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at Accessed October 2015.

(© 1995–2015). Electrolyte Panel, Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at Accessed October 2015.

Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Carlson, R. and Abbas, A. (2001). Use Of Anion Gap In Acid-Base Defects In The Acutely Ill. Medical Online Review and Database, Snow Tiger Medical Systems [On-line information]. Available online at

Martin, L. (1999 February). 2. Anion and bicarbonate gaps for diagnosing mixed acid-base disorders. All You Really Need to Know to Interpret Arterial Blood Gases [On-line, Ch 2 of book published by Lippincott Williams & Wilkins]. Available online at

Fall, P. (2000 March). A stepwise approach to acid-base disorders, Practical patient evaluation for metabolic acidosis and other conditions. Postgraduate Medicine online, 107 (3) [On-line journal]. Available online at

Brandis, K. (2002 August 14) 3.2 The Anion Gap. Acid-Base Physiology [On-line textbook]. Available online at

Brandis, K. (2002 August 14) 3.4 The Urinary Anion Gap. Acid-Base Physiology [On-line textbook]. Available online at

Harrison, J. (1997 January 5, Modified). Metabolic (including renal) Acid-Base Imbalance. Tulane Medical Pathology Course [On-line information]. Available online at

(2003) Anion Gap. Michigan State Univ, Dept of Physiology [On-line information for class 442]. Available online: at

(1995-2004). Chapter 59. Disorders of Acid-Base Metabolism. The Merck Manual of Geriatrics [On-line information]. Available online at

(1995-2004). Acid-Base Metabolism. The Merck Manual of Diagnosis and Therapy, Section 2. Endocrine And Metabolic Disorders, Chapter 12. Water, Electrolyte, Mineral, And Acid-Base Metabolism [On-line information]. Available online at

Hornick, D., Editor (2003, Revised). An Approach to the Analysis of Arterial Blood Gases and Acid-Base Disorders. Virtual Hospital, University of Iowa Health Care [On-line information]. Available online at

Priestley, M. and Lieh-Lai, M. (2004 March 8, Updated). Excerpt from Acidosis, Metabolic. EMedicine [On-line information]. Available online at

Jones, J. and Bosker, G. (2002 December 16) Diagnostic Aids in Emergency Medicine. The Emergency Medicine Reports Textbook of Adult and Pediatric Emergency Medicine [Excerpt from On-line Clinical Textbook]. Available online at and

Beaven, A. (2002 July 12). Ethylene Glycol and Methanol Toxicity. Univ of NC at Chapel Hill, Department of Internal Medicine [On-line information]. PDF available for download at

(2002). Acid-Base Emergencies, Part 1. Texas Society for Respiratory Care [On-line information]. Available online at

Welch, J. (1998 April 30, Modified). Increased Anion Gap Metabolic Acidosis. Georgetown University, NetScut [On-line information]. Available online at

Welch, J. (1998 April 30, Modified). Normal Anion Gap Metabolic Acidosis. Georgetown University, NetScut [On-line information]. Available online at

(1995-2004). Minerals and Electrolytes. The Merck Manual of Medical Information – Second Home Edition [On-line information]. Available online at

Ben-Joseph, E., Reviewed (2004 July). Dehydration. Information for Parents [On-line information]. Available online at

Webner, D., Updated (2003 August 18). CO2. MedlinePlus Medical Encyclopedia [On-line information]. Available online at

A.D.A.M. editorial, Updated (2003 October 15). Electrolytes. MedlinePlus Medical Encyclopedia [On-line information]. Available online at

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry. AACC Press, Washington, DC. Pp 333-337.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007.

(August 14, 2007). MedlinePlus Medical Encyclopedia, Electrolytes. Available online at Accessed May 2008.

ARUP Lab Tests. Electrolyte Panel. Available online at Accessed September 2011. 

Mayo Medical Laboratories. 87972 Overview: Electrolyte Panel, Serum. Available online at Accessed September 2011.

Ask a Laboratory Scientist

lab scientist

Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, the American Society for Clinical Laboratory Science (ASCLS). Click on the Contact a Scientist button below to be re-directed to the ASCLS site to complete a request form. If your question relates to this web site and not to a specific lab test, please submit it via our Contact Us page instead. Thank you.

Contact a Scientist