Anion gap
The anion gap is a medical diagnostic tool used to assess the balance of positively and negatively charged electrolytes in the blood. It is calculated from the results of an electrolyte panel and indicates the presence of acid-base imbalances. A high anion gap suggests acidosis, which can arise from various conditions such as diabetic ketoacidosis, excessive alcohol consumption, or prolonged diarrhea, often leading to symptoms like nausea, difficulty breathing, and confusion. Conversely, a low anion gap, which is less common, may indicate alkalosis, often due to conditions like hypoalbuminemia caused by malnutrition or kidney disease, presenting symptoms such as dizziness and muscle spasms. Identifying the anion gap is crucial for healthcare providers, as it can signal serious underlying health issues that require prompt intervention. Further tests may be ordered to pinpoint the specific electrolyte imbalance and guide appropriate treatment. Understanding the anion gap can be vital for recognizing potential health crises and facilitating timely medical responses.
On this Page
Subject Terms
Anion gap
The anion gap is an assessment of blood test results that compares the negatively and positively charged electrolytes in a person’s blood. If the difference between the negative and positive levels is high or low compared to normal levels, it can indicate a problem with the patient’s health. High levels mean the blood is too acidic. A low level, which is rarer, can indicate that the blood is too alkaline.
Background
Water is very important to the function and health of the human body. Water is a key component of blood and is found both in and around the body’s cells. Minerals known as electrolytes help the body keep the right amount of water in the right places to maintain optimal health. Having an electrical charge, electrolytes also help maintain the body’s level of acids. Many acids are present in the body and help it function properly. Some acids in the body include amino acids, fatty acids, ascorbic acid, and hydrochloric acid. Electrolytes include sodium, potassium, chloride, and bicarbonate.
Electrolytes are found in the body’s cells, and they attract water to the cells. When there are many electrolytes in a cell, more water will enter. When the electrolyte level drops low, water will leave the cells. The kidneys help maintain this level by filtering both water and electrolytes, removing some and sending the rest back into the body.
The amount of these electrolytes in the body can be measured by performing a blood test known as an electrolyte panel. A needle is used to remove a small amount of blood from a vein in the patient’s arm. This is then tested in a laboratory to determine the levels of various types of electrolytes that are present.
All electrolytes have either a positive or a negative electrical charge. When the electrolytes are in balance, the body can function normally. When the electrolytes are unbalanced, they affect the levels of acid in the blood. This is known as a pH imbalance. A pH reading is a scale that measures how much acid or base is in water or a solution.
Overview
In addition to measuring the amounts of electrolytes in the blood, physicians compare the levels of positive and negative electrolytes as identified by the electrolyte panel. They use a specific formula to calculate the difference. This difference between the amounts of these levels is known as the serum anion gap, or simply the anion gap.
The anion gap helps the physician know if the body has too much acid or too little base. Acidosis is a condition present in the body if a patient has reduced alkalinity (base) and too much acid. The anion gap can also alert the physician that the body has too little acid, a condition known as alkalosis. Both conditions indicate that the person could have a serious health condition that needs treatment.
A high anion gap indicates that the patient might have acidosis. Acidosis can occur for a number of reasons. One is when the body makes too much acid. Diabetic patients can produce acids called ketones. People who exercise too much can produce high amounts of lactic acid. In addition, people who ingest poisons such as antifreeze, who consume excessive amounts of alcohol or overdose on drugs, or who ingest too much aspirin can develop high levels of acid in the blood. People who have diarrhea for a long time and people who have kidney problems can all have high levels because they lose too much of the electrolyte bicarbonate. People with acidosis might experience breathing difficulties, nausea, edema (swelling), fast or irregular heartbeats, low blood pressure, weakness, and confusion.
A low anion gap is much less common. It so often is the result of a mistake in the test that physicians routinely order repeat tests when a low anion gap is reported. When it is confirmed, it indicates the patient has alkalosis.
Alkalosis occurs when the body has too little acid. One of the most frequent causes is a condition called hypoalbuminemia. Albumin is a protein that is essential to human life. Some conditions cause the albumin to leak out of the cells and blood vessels, and to be removed by the kidneys. This can cause levels to drop in the patient. Some conditions that can cause this to happen include malnutrition, severe burns, sepsis or blood infections, liver or kidney disease, recent surgery, multiple myeloma, and some other conditions that cause inflammation or irritation to cells in the body. Symptoms that indicate a person might have alkalosis include dizziness, difficulty breathing, seizures, muscle spasms, heart palpitations, overall weakness, and delirium.
The anion gap alerts the physician to the presence of these conditions, some of which are life-threatening and require immediate treatment. Once the anion gap has indicated the condition, the physician will order additional blood tests to identify which electrolytes are out of balance. The physician may order other additional tests, including tests to identify blood gases and tests that measure levels of substances such as lactate, glucose, creatinine, and blood urea nitrogen. If poisoning is suspected, blood tests may also be performed to identify the type and amount of the poison that was ingested.
Once the cause is identified, the physician will order treatments to address the specific reason for the anion gap. For example, if the patient is diabetic and has ketoacidosis that is identified by a high anion gap and confirmed by other tests, the patient might be put on medication to lower his or her blood sugar levels and address the diabetes. This should result in a drop in the patient’s blood acids and, eventually, in a more normal anion gap.
Bibliography
“Anion Gap.” Medscape, 13 Mar. 2014, emedicine.medscape.com/article/2087291-overview. Accessed 26 Oct. 2018.
“Anion Gap.” University of Rochester Medical Center Health Encyclopedia, www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=anion‗gap‗blood. Accessed 26 Oct. 2018.
Brodkey, Frank. “Tales of the Anion Gap, Part I.” MD Magazine,8 Sept. 2014, www.mdmag.com/contributor/frank-brodkey/2014/09/tales-of-the-anion-gap-part-i. Accessed 26 Oct. 2018.
Brodkey, Frank. “Tales of the Anion Gap, Part II: Metabolic Acidosis.” MD Magazine, 29 Sept. 2014, www.mdmag.com/contributor/frank-brodkey/2014/09/tales-of-the-anion-gap-part-ii. Accessed 26 Oct. 2018.
Brodkey, Frank. “Tales of the Anion Gap, Part III: Case Examples.” MD Magazine, 21 Oct. 2014, www.mdmag.com/contributor/frank-brodkey/2014/10/tales-of-the-anion-gap-part-iii-case-examples. Accessed 26 Oct. 2018.
Lewis, James L. “Overview of Electrolytes.” Merck Manual, www.merckmanuals.com/home/hormonal-and-metabolic-disorders/electrolyte-balance/overview-of-electrolytes. Accessed 26 Oct. 2018.
Seladi-Schulman, Jill. “What Does a Low Anion Gap Mean?” Healthline, 7 Nov. 2017, https://www.healthline.com/health/low-anion-gap. Accessed 26 Oct. 2018.
Smith, Lori. “Low Anion Gap: Causes, Test, and Treatment.” Medical News Today, 16 Apr. 2018, www.medicalnewstoday.com/articles/321512.ph. Accessed 26 Oct. 2018.