Anion Gap

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Update Date 12/05/2020
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Know the basics

What is Anion Gap?

Anion gap (AG) is the difference between the cations and anions in extracellular portion. Anion gap often is measured in the laboratory. (For example, AG = [Na + + K +] – [Cl- + HCO3-])

These calculations allow doctors to identify the cause of your infection such as metabolic acidosis caused by accumulation of lactic acid (a complication of shock due to excessive blood loss, or difficulty breathing) or by the accumulation of ketones in blood (a complication of diabetes) and test shows the amount of bicarbonate to neutralize them and maintain the pH in blood.

Why is Anion Gap performed?

Calculate the anion gap to assess patients with disorders related to alkali or acidosis in blood. The test is used to determine cause of disturbances, and also to monitor treatment of acid-base disorders. Doctors use this test to find out some of the following diseases:

  • DKA due to diabetes;
  • Salicylic acid poisoning;
  • Accumulation of lactic acid due to excessive blood loss, or difficulty breathing;
  • Kidney failure;
  • Dehydration and ions loss from the gastrointestinal tract due to vomiting or sweat;
  • Take water and ions through the kidneys.

Things to know before

What should I know before receiving Anion Gap?

These factors may affect test results, such as:

  • Hyperlipidemia can cause measured sodium reduction and reduce the anion gap than actuality.
  • Normal value of anion gap is not the same in laboratories, because each uses different measurement methods. Normally, laboratories will be printed normal value with the test results.
  • Drugs increase space such as carbon anhydrase inhibitors, ethanol, methanol, and salicylate.
  • The gap relievers such as acetazolamide, lithium, spironolactone, and sulindac

It is important you understand the warnings and precautions before having this surgery. If you have any questions, please consult with your doctor for more information and instructions.

Know what happens

How to prepare for Anion Gap?

Your doctor will explain testing procedures for you. In fact, agglutinins test is a blood test. You do not need any special preparation before the test. You do not have to fast before collecting blood for testing.

You should wear a short sleeve shirt in order to nurse can easily take blood from your arm.

What happens during Anion Gap?

To implement the test, doctor will:

  • Bandage around arm to stop bleeding
  • Disinfect the injection site with alcohol
  • Inject needle into vein. They could inject more than 1 time if necessary
  • Attach a hose to contain bleeding
  • Remove the strips of tape around the arm after getting enough blood
  • Put bandage or a cotton swab on the injection site
  • Put urgo on the injection site

What happens after Anion Gap?

Doctors or nurse will take blood for the test. Your pain degree depends on skills of nurses, your venous situation and your sensitivity to pain.

After taking blood, you need to put bandage and press lightly on needle puncture to stop bleeding. You can return to normal activity after the test.

If you have any questions about the Anion gap, please consult with your doctor to better understand your instructions.

Understand the results

What do my results mean?

Normal result:

  • 16 ± 4 mEq / L (if Potassium is used in the calculation);
  • 12 ± 4 mEq / L (if Potassium is not used in the calculation.).

Abnormally increasing result:

  • Lactic acidosis;
  • ketones due to diabetic acidosis;
  • ketones acidosis due to alcohol;
  • Lack of food;
  • kidney failure;
  • renal tubular acidosis;
  • Increase the amount of bicarbonate loss through the gastrointestinal tract;
  • Reduced aldosterone syndrome.

Abnormally decreasing result:

  • Controlling excessive digestive chemicals;
  • Multiple myeloma bone;
  • Prolonged vomiting;
  • Rinse the stomach;
  • Reduce blood protein;
  • lithium toxicity;
  • Bromine poisoning (from grenadine).

Depending on the laboratory and hospital, the normal range for Anion gap may vary. Please discuss with your doctor any questions you may have about your test results.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Read also:


    Ferri, Fred. Ferri’s Netter Patient Advisor. Philadelphia, PA: Saunders / Elsevier, 2012. Print edition. Page 869
    Porter, R. S., Kaplan, J. L., Homeier, B. P., & Albert, R. K. (2009). The Merck manual home health handbook. Whitehouse Station, NJ, Merck Research Laboratories. Print edition. Page 876
    Anorexia Nervosa Fact Sheet. Accessed July 15, 2016.
    Anorexia Nervosa: MedlinePlus Medical Encyclopedia. National Library of Medicine - National Institutes of Complementary, alternative, or integrative health: What's in a name? National Center for Complementary and Alternative Medicine. Accessed July 15, 2016.
    Eating Disorders: About More Than Food. NIMH. Accessed July 15, 2016.
    Health. Accessed July 15, 2016.

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