Anion Gap Blood Test
Reviewed
Also called: Serum Anion Gap, AG Blood Test
An anion gap blood test gives a measurement of the acid-base balance (pH balance) in your blood.
Specimen: Blood
Why this test may be ordered
- To check for an electrolyte imbalance
- If you have symptoms of acidosis such as shortness of breath, vomiting, confusion, fatigue, or fast heartbeat
- If you have symptoms of alkalosis such as arrhythmia, irritability, hand tremor, muscle twitching, nausea, vomiting, or numbness/tingling in the face, hands, or feet
Preparation and collection
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.
The anion gap test is a calculation that's done with the results of an electrolyte panel, which is a blood test. During a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle.
There is very little risk to having this test. You may feel slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
Normal results may vary by lab. Several types of medical conditions can cause abnormal anion gap test results. Your provider will use the results of this test, your medical history, and other tests to make a diagnosis.
- High anion gap: A high anion gap test result may mean that you may have acidosis, which may be caused by: Dehydration, Diarrhea, Too much exercise, Kidney diseases, Diabetes or diabetic ketoacidosis, Salicylate poisoning, for example from too much aspirin, Antifreeze poisoning. Limitation: But there is a wide range of normal results and many possible causes of abnormal results. Next step: Your provider will use the results of this test, your medical history, and other tests to make a diagnosis.
- Low anion gap: A low anion gap test result may mean you have alkalosis. The most common cause of a low anion gap is a low level of albumin, a protein in the blood. Limitation: But this result is so rare that your provider will usually have you tested again to make sure the results are accurate. Next step: So, talk with your provider about what your test results mean and whether you need additional testing to make a diagnosis.
- There is a wide range of normal results and many possible causes of abnormal results.
- The anion gap test is a calculation based on other electrolyte tests, so its accuracy depends on those measurements.
- A low anion gap result is rare and often requires repeat testing to confirm.
What to do next
So, talk with your provider about what your test results mean and whether you need additional testing to make a diagnosis.
- What do my anion gap results indicate about my acid-base balance?
- Do I need any follow-up tests based on these results?
- What symptoms should I watch for that might relate to acidosis or alkalosis?
- How do my other health conditions or medications affect these results?
- Should I make any changes to my diet or lifestyle based on this test?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.