Leave blank for the usual potassium-omitted form.
Add albumin to also get the corrected gap. 40 g/L is 4.0 g/dL.
The equation, and where it comes from
AG = Na⁺ - (Cl⁻ + HCO₃⁻) · corrected AG = AG + 2.5 x (4.0 - albumin g/dL)
Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807-1810, for the 2.5 mEq/L per g/dL albumin correction.
How to read the result
Reference range on modern analysers is roughly 3 to 11 mEq/L with potassium omitted, lower than the 8 to 12 quoted in older texts because chloride and bicarbonate assays changed. Check your own laboratory's range.
Your patient's numbers never leave this device
The anion gap arithmetic runs in JavaScript inside your own browser. There is no server call when you type, nothing is written to a database, nothing is logged, and no account is involved. Once the page has loaded you can disconnect from the network and it still works.
That matters more here than on an ordinary calculator. Values entered on a hospital workstation come off a real chart, and this tool deliberately does not remember them: close the tab and they are gone, including for the next person who uses that machine.
Frequently asked questions
- How do you calculate the anion gap?
- Anion gap = sodium - (chloride + bicarbonate). Some units add potassium to the cation side, giving (sodium + potassium) - (chloride + bicarbonate), which runs about 4 mEq/L higher. This calculator does either: leave the potassium field blank for the more common form.
- Why correct the anion gap for albumin?
- Albumin is the largest unmeasured anion in serum, so a low albumin shrinks the measured gap and can hide a genuine high-gap acidosis. The usual correction adds 2.5 mEq/L for every 1 g/dL the albumin sits below 4.0. In a critically ill patient with an albumin of 2, an apparently normal gap of 11 corrects to 16.
- What is a normal anion gap?
- Roughly 3 to 11 mEq/L with potassium omitted on contemporary analysers. Older textbooks quote 8 to 12, and the drop is a measurement artefact rather than a change in physiology: ion-selective electrodes report chloride differently from the older methods. Use your own laboratory's stated interval where you have it.
- What is the delta ratio and when does this tool show it?
- The delta ratio compares the rise in the anion gap with the fall in bicarbonate, which helps show whether a second acid-base disorder sits alongside a high-gap acidosis. It is only interpretable when the gap is actually raised, so this calculator shows it only above a gap of 12 rather than printing a meaningless number.
- Are my lab values sent to a server?
- No. The whole calculation is JavaScript running in your browser. Nothing is transmitted, nothing is stored, and no account is involved. That matters more here than on a general-purpose calculator, because these are values from a real patient's chart.