Anion Gap Blood Test

What is Anion Gap Test?

An anion gap blood test is a way to check the levels of acid in your blood. The anion gap is a value that’s calculated using the results of an electrolyte blood test. 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

Why You Need Anion Gap Test

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 AGAP Blood test Done?

To detect a problem with your body’s electrolyte balance

When To Get Tested?

As part of routine health screening or when your healthcare practitioner 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?


Symptoms of 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:

  • nausea or vomiting
  • fatigue
  • a headache
  • drowsiness
  • shortness of breath
  • rapid heart rate
  • low blood pressure

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.

Causes of a low anion gap

Normally, anion gap results range from 3 to 10 milliequivalents per liter (mEq/L).

Several underlying conditions can result in a pH imbalance and cause an abnormal anion gap.

A low anion gap is very rare. If an electrolyte test shows a low anion gap, a doctor will usually order a second test, as the results may be due to a laboratory error.

Other than a laboratory error, a less common cause of a low anion gap is hypoalbuminemia.

Causes of a high anion gap

When a person has too much acid or too little base in their blood, the anion gap will be higher than normal. This is called acidosis and can be life-threatening in some situations.

Acidosis can be caused by a variety of conditions, including:

  • some lung disorders, such as severe asthma, sleep apnea, pneumothorax, myasthenia gravis, botulism, amyotrophic lateral sclerosis (ALS), and Guillain-Barre syndrome
  • uncontrolled diabetes or diabetic ketoacidosis
  • kidney damage or failure
  • prolonged diarrhea
  • starvation
  • excessive alcohol use that causes alcoholic ketoacidosis
  • lactic acidosis, which is a buildup of lactic acid
  • exposure to high levels of salicylates (aspirin), methanol, ethylene glycol, or antifreeze
  • drug overdose

Treatment of Anion Gap

Treatment for an abnormal anion gap will focus on the underlying cause.

A low or high anion gap alone cannot diagnose a medical condition, so a doctor will perform a variety of other tests before making a treatment plan. Treatment for low anion gap is focused on treating the underlying cause.

If your test results come back indicating a low anion gap, your doctor may want to repeat the test to account for laboratory error. Once a low anion gap has been confirmed, your doctor will order additional tests to determine the underlying cause of the result.

Anyone concerned about a high or low anion gap in their blood test results may find it helpful to speak with a doctor about the potential cause.

If you’re taking medication that can lead to a low anion gap, such as lithium or medication containing bromide, you can talk to your doctor about adjusting the dosage, if possible.

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.

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