Anion Gap Blood Test

An anion gap blood test gives a measurement of the acid-base balance (pH balance) in your blood. This lets you know whether your blood is too acidic or not acidic enough. The test also checks for an electrolyte imbalance in your blood.

To do the measurement, an anion gap test uses the results of an electrolyte panel or other blood tests that measure your electrolytes. Electrolytes are minerals that have an electrical charge when they are dissolved in water or body fluids. You get them from the foods you eat and the fluids you drink.

You have electrolytes in your blood, urine, tissues, and other body fluids. They help control the acid-base balance of your blood. A few of your body's electrolytes that are often measured in your blood include sodium, chloride, potassium, and bicarbonate.

Some electrolytes have a positive electric charge. Others have a negative electric charge. The anion gap measures the difference—or gap—between the negatively charged and positively charged electrolytes in your blood.

If the anion gap is too high, your blood is more acidic than normal. If the anion gap is too low, your blood isn't acidic enough. Both high and low results may be signs of a serious disorder that needs attention.

Why this test is done

Your health care provider may order an anion gap blood test if you have symptoms of acidosis or alkalosis. Symptoms may vary depending on the underlying disease or condition.

Symptoms of acidosis may include:

• Shortness of breath
• Vomiting
• Confusion
• Fatigue
• Tachycardia (very fast heartbeat)

Symptoms of alkalosis may include:

• Arrhythmia (a problem with the rate or rhythm of your heartbeat)
• Irritability
• Hand tremor
• Muscle twitching
• Nausea, vomiting
• Numbness or tingling in the face, hands, or feet

How to prepare

No special preparation is necessary for an anion gap blood test. If your provider has ordered more tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions.

Sample type

Blood

Other names for this test

Serum anion gap