Anion Gap Blood Test
Reviewed
An anion gap blood test measures the acid-base balance (pH balance) in your blood by calculating the difference between negatively and positively charged electrolytes. It helps detect if your blood is too acidic (acidosis) or not acidic enough (alkalosis).
Preparation and collection
No special preparation is necessary for this test. If your provider has ordered more tests on your blood sample, you may need to fast for several hours before the test. Your provider will let you know if there are any special instructions.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- 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
Talk with your provider about what your test results mean and whether you need additional testing to make a diagnosis.