Anion Gap Blood Test

What does anion gap mean in a blood test?

Anion gap (or serum anion gap) is a measurement to check for how acidic your blood is. Too much acid or too little acid in your blood can be a sign of certain health conditions.

The anion gap is a calculation of the difference between the amounts of negatively charged electrolytes and the amount of positively charged electrolytes in your blood. The gap between the two is your anion gap.

Your healthcare provider uses the results of other blood tests to determine your anion gap. These blood tests are commonly included in routine bloodwork panels:

• Comprehensive metabolic panel (CMP).
• Basic metabolic panel (BMP).
• Electrolyte panel.

What is an anion gap blood test used for?

The anion gap reveals whether your blood has an imbalance of electrolytes or if your blood is too acidic or too basic. If you have too much acid in your blood, it’s called acidosis. If your blood is too basic, you may have alkalosis. Both can be dangerous because it means something in your body isn’t working correctly. Your provider will use the results to get to the bottom of what’s causing a high or low anion gap result.

When would I need an anion gap blood test?

Your healthcare provider may order a blood panel that includes an anion gap test if you have signs and symptoms of an imbalance in your blood acid levels — either acidosis (too acidic) or alkalosis (too basic).

Sometimes, the anion gap is included in routine bloodwork you may be getting for another reason. In these instances, you don’t have symptoms or signs of a problem, but the anion gap is included in your test results anyway. The following tests may show an anion gap result:

• Basic metabolic panel (BMP).
• Comprehensive metabolic panel (CMP).
• Electrolyte panel.
• Renal function panel (RFP).

How does the test work?

Laboratory scientists calculate anion gap from the results of any blood panel with sodium, chloride and CO2. The results may explain why you have uncomfortable symptoms from your blood being too acidic or not acidic enough (basic). They can use your anion gap to help determine if you have an underlying health condition.

How do I prepare for an anion gap blood test?

Your healthcare provider will tell you if you need to prepare for the blood test. This may include avoiding eating and drinking (fasting) for several hours before your blood draw. Let your provider know if you’re taking any medications as they could alter your test results.

What should I expect during the test?

You can expect to experience the following during a blood test, or blood draw:

1. You’ll sit in a chair and a phlebotomist will check your arms for an easily accessible vein. They may use an elastic band to start the flow of blood to a vein. This is usually in the inner part of your arm on the other side of your elbow.
2. Once they’ve located a vein, they’ll clean and disinfect the area.
3. They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
4. After they insert the needle, a small amount of blood will collect in a test tube.
5. Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
6. They’ll place a bandage over the site, and you’ll be finished.

The entire procedure usually takes less than five minutes.

What should I expect after my anion gap test?

A provider sends your blood sample to a laboratory for testing. Then, a medical laboratory scientist prepares the sample and performs the test on machines known as blood analyzers.

Once the test results are back, your healthcare provider will share the results with you or put the results in your electronic medical record.

What are the risks of an anion gap blood test?

Blood tests are a very common and essential part of medical testing. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this will go away within a day or two.

What do the results of an anion gap blood test mean?

Blood test reports, including anion gap blood test results, usually provide the following information:

• The name of the blood test or what was measured in your blood.
• The number or measurement of your blood test result.
• The normal measurement range for that test.
• If your result is normal or abnormal or high or low.

What is a normal anion gap blood test result?

There’s no universal “normal” anion gap. Once you get your blood test results back, there will be information that indicates what that lab’s normal anion gap range is.

There’s also a wide range of “normal” anion gap results depending on different factors. For example, people who take lithium carbonate medication for bipolar disorder may have a reduced anion gap due to the medication.

What does a high anion gap mean?

If your blood test results show a high anion gap, you may have acidosis. This means you may have a higher-than-normal level of acid in your blood (a lower-than-normal blood pH).

Acidosis may be a sign of the following:

• Dehydration.
• Diarrhea.
• Too much exercise.

Having acidosis may also indicate more serious conditions, including:

• Kidney disease: Healthy kidneys remove acid from your body through your pee. But if you have kidney disease, your kidneys can’t remove enough acid, which can lead to metabolic acidosis.
• Diabetes: Acidosis could indicate that you have undiagnosed Type 1 diabetes. When your pancreas no longer makes enough insulin to allow blood sugar into your cells, it can make your blood acidic.
• Diabetes-related ketoacidosis (DKA): This is a life-threatening complication of undiagnosed diabetes due to lack of insulin.
• Salicylate poisoning (salicylate toxicity): Salicylates are a type of drug found in many over-the-counter (OTC) and prescription medications. Aspirin is the most common type of salicylate. Ingesting too much or overdosing on salicylates can cause salicylate poisoning, which is life-threatening.

What does a low anion gap blood mean?

Having a low anion gap blood test result is rare. Because of this, your provider will likely redo the test to make sure the results are accurate.

If your blood results reveal a low anion gap, it may mean you have a lower-than-normal level of albumin (hypoalbuminemia). Albumin is an essential protein in your blood. Low albumin may indicate the following conditions:

• Kidney issues.
• Heart disease.
• Liver disease.
• Certain types of cancer.

Again, low anion gap results are uncommon. Be sure to talk to your provider for more information on your test results.

Should I be concerned if I have a low or high anion gap?

If your blood test results reveal that you have a high or low anion gap, it doesn’t necessarily mean you have a medical condition. Many factors can affect your electrolyte levels, which affect your anion gap measurement. There could’ve also been an error in the collection, transport or processing of the blood tests.

When your healthcare provider interprets your blood test results, they consider many factors, such as your medical history and medications. Your provider may recommend additional testing to determine a diagnosis if your anion gap results are abnormal. Nobody looks forward to blood tests, especially getting them so close together, but it’s the best way to make sure your electrolytes are at the expected levels.

If you have any questions about your results, be sure to ask your provider.

When should I know the results of an anion gap blood test?

If you have signs and symptoms of acidosis, such as shortness of breath and vomiting, your provider will draw your blood for an anion gap blood test as soon as possible. They’ll likely have the results within a few hours.

If your anion gap test is part of a routine bloodwork panel, such as a basic metabolic panel, it could take one to two business days to get the results.