What is an Anion Gap Blood Test?
An anion gap blood test is a way to check the levels of acid in your blood. The test is based on the results of another blood test called an electrolyte panel. Electrolytes are electrically charged minerals that help control the balance of chemicals in your body called acids and bases. Some of these minerals have a positive electric charge. Others have a negative electric charge. The anion gap is a measurement of the difference-or gap-between the negatively charged and positively charged electrolytes. If the anion gap is either too high or too low, it may be a sign of a disorder in your lungs, kidneys, or other organ systems.
Other names: Serum anion gap
What is it used for?
The anion gap blood test is used to show whether your blood has an imbalance of electrolytes or too much or not enough acid. Too much acid in the blood is called acidosis. If your blood does not have enough acid, you may have a condition called alkalosis.
Why do I need an anion gap blood test?
Your health care provider may have ordered an anion gap blood test if you have signs of an imbalance in your blood acid levels. These signs may include:
What happens during an anion gap blood test?
The anion gap test is taken from the results of an electrolyte panel, which is a blood test. During a blood test, a health care professional uses a small needle to take a blood sample from a vein in your arm. After the needle is inserted, a small amount of blood will be collected into a test tube. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
You don't need any special preparations for an anion gap blood test. If your health care provider has also ordered other blood tests, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.
Are there any risks to the test?
There is very little risk to having this test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
If your results show a high anion gap, you may have acidosis, which means higher than normal levels of acid in the blood. Acidosis may be a sign of dehydration, diarrhea, or too much exercise. It may also indicate a more serious condition such as kidney disease or diabetes.
If your results show a low anion gap, it may mean you have a low level of albumin, a protein in the blood. Low albumin may indicate kidney problems, heart disease, or some types of cancer. Since low anion gap results are uncommon, retesting is often done to ensure the results are accurate. Talk to your health care provider to learn what your results mean.
Is there anything else I need to know about an anion gap blood test?
The anion gap blood test can provide important information about the acid and base balance in your blood. But there are a wide range of normal results, so your health care provider may recommend additional testing to make a diagnosis.
- ChemoCare.com [Internet]. Cleveland (OH): ChemoCare.com; c2002-2017. Hypoalbuminemia (Low Albumin) [cited 2017 Feb 1]; [about 3 screens]. Available from: http://chemocare.com/chemotherapy/side-effects/hypoalbuminemia-low-albumin.aspx
- Evidence-Based Medicine Consult [Internet]. EBM Consult, LLC; Lab Test: Anion Gap; [cited 2017 Feb 1]; [about 2 screens]. Available from: http://www.ebmconsult.com/articles/lab-test-anion-gap
- Galla J. Metabolic Alkalosis. Journal of the American Society of Nephrology [Internet]. 2000 Feb 1 [cited 2017 Feb 1]; 11 (2): 369-75. Available from: http://jasn.asnjournals.org/content/11/2/369.full
- Kraut JA, Madias N. Serum Anion Gap: Its Uses and Limitations in Clinical Medicine. Clinical Journal of the American Society of Nephrology [Internet]. 2007 Jan [cited 2017 Feb 1]; 2 (1):162–74. Available from: http://cjasn.asnjournals.org/content/2/1/162.full.pdf
- Kraut JA, Nagami GT. The serum anion gap in the evaluation of acid-base disorders: What are its limitations and can its effectiveness be improved?; Clinical Journal of the American Society of Nephrology [Internet]. 2013 Nov [cited 2017 Feb 1]; 8 (11):2018–24. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23833313
- Lab Tests Online [Internet]. Washington D.C.: American Association for Clinical Chemistry; c2001–2017. Electrolytes; [updated 2015 Dec 2; cited 2017 Feb1]; [about 3 screens]. Available from: https://labtestsonline.org/understanding/analytes/electrolytes/tab/test
- Lolekha PH, Vanavanan S, Lolekha S. Update on value of the anion gap in clinical diagnosis and laboratory evaluation. Clinica Chimica Acta [Internet]. 2001 May [cited 2016 Nov 16]; 307(1–2):33–6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/11369334
- Merck Manuals [Internet]. Kenilworth (NJ): Merck & Co., Inc.; c2016. Consumer Version: Overview of Acid-Base Balance; [updated 2016 May; cited 2017 Feb 1]; [about 2 screens]. Available from: https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/acid-base-balance/overview-of-acid-base-balance
- Merck Manuals: Professional Version [Internet]. Kenilworth (NJ): Merck & Co., Inc.; c2016. Acid-Base Disorders; [cited 2017 Feb 1]; [about 2 screens]. Available from: http://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/acid-base-regulation-and-disorders/acid-base-disorders
- National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Types of Blood Tests; [updated 2012 Jan 6; cited 2017 Feb 1]; [about 4 screens]. Available from: http://www.nhlbi.nih.gov/health/health-topics/topics/bdt/types
- National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What Are the Risks of Blood Tests?; [updated 2012 Jan 6; cited 2017 Feb 1]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/risks
- National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What To Expect with Blood Tests; [updated 2012 Jan 6; cited 2017 Jan 31]; [about 4 screens]. Available from: https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/with
- University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2017. Health Encyclopedia: Anion Gap (Blood); [cited 2017 Feb 1]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=anion_gap_blood
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The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.In the event of a medical emergency, call 911 immediately.