Anion gap blood test
In short
A typical adult anion gap result is 7 to 13 mmol/L. A slightly high anion gap is common and often means little by itself. It matters more when CO2 is low at the same time. Always read your result against the range printed on your own report.
A calculated number that checks the blood's acid balance.
The anion gap is a calculation, not a measurement. It compares positively and negatively charged salts in your blood, using sodium, chloride and CO2 (bicarbonate). A high gap can point to extra acids, which helps doctors explain a low CO2.
Is my Anion gap high or low?
Type your result to see where it sits.
Nothing you type leaves this device.
Typical range
| For | Range | Unit |
|---|---|---|
| Adults | 7–13 | mmol/L |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your Anion gap is high
A slightly high anion gap is common and often means little by itself. It matters more when CO2 is low at the same time.
Common reasons
- Not drinking enough
- Hard exercise shortly before the test
- Fasting or a very low-carb diet, which makes acids called ketones
- Kidneys that do not clear acid well
- Less often: acid buildup from uncontrolled diabetes or a serious illness
- Less often: swallowing a toxic substance, such as antifreeze
If your Anion gap is low
A low anion gap is uncommon and most often reflects low albumin, a main blood protein. It can also come from differences in lab methods.
Common reasons
- Low albumin, a main blood protein
- Differences in how labs measure it
- Less often: an excess of one antibody protein, as in myeloma, a blood cancer
What can throw it off
Low albumin, a main blood protein, pulls the anion gap down, so doctors adjust for it.
Questions to take to your appointment
- 1Is my CO2 low too, or is this gap on its own?
- 2Should my albumin be taken into account?
Read together with
Doctors rarely read Anion gap alone. These usually sit next to it.
- CO2Mostly bicarbonate, which keeps your blood from becoming too acidic.
- SodiumA mineral salt (electrolyte) that keeps the body's water in balance.
- ChlorideA mineral salt (electrolyte) that works with sodium to balance fluids.
- AlbuminThe main protein in blood, made by the liver.
- GlucoseThe sugar in your blood, your body's main fuel.
Quick answers
What is the anion gap blood test?
Anion gap: A calculated number that checks the blood's acid balance. The anion gap is a calculation, not a measurement. It compares positively and negatively charged salts in your blood, using sodium, chloride and CO2 (bicarbonate). A high gap can point to extra acids, which helps doctors explain a low CO2.
What is a normal anion gap level?
For most adults, anion gap is typically 7 to 13 mmol/L. Labs differ a little, so the range printed next to your result is the one to go by.
What does a high anion gap mean?
A slightly high anion gap is common and often means little by itself. It matters more when CO2 is low at the same time. Common reasons include not drinking enough; hard exercise shortly before the test; fasting or a very low-carb diet, which makes acids called ketones; and kidneys that do not clear acid well. A doctor reads it together with your other results and how you feel.
What does a low anion gap mean?
A low anion gap is uncommon and most often reflects low albumin, a main blood protein. It can also come from differences in lab methods. Common reasons include low albumin, a main blood protein; differences in how labs measure it; and less often: an excess of one antibody protein, as in myeloma, a blood cancer.
What can affect my anion gap result?
Low albumin, a main blood protein, pulls the anion gap down, so doctors adjust for it.
What should I ask my doctor about my anion gap?
Questions worth taking to the appointment: Is my CO2 low too, or is this gap on its own? Should my albumin be taken into account?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
Vita: Health Coach on the App StoreSources
Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.