Albumin-Corrected Anion Gap CalculatorFree online fitness & health calculator — instant results, no sign-up
Adjust a measured anion gap for serum albumin using the Figge approximation.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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About the Albumin-Corrected Anion Gap Calculator
The Albumin-Corrected Anion Gap Calculator adjusts a measured anion gap for serum albumin using the Figge approximation. Because albumin contributes to the anion gap, a low albumin level can make the measured gap appear lower than it otherwise would. This tool estimates the gap corrected to an albumin concentration of 4 g/dL for educational use in adults.
- Measured anion gap (mmol/L)
- The measured anion gap is the electrolyte-derived value reported or calculated from your laboratory results, entered in mmol/L with a default of 12.
- Serum albumin (g/dL)
- Serum albumin is the blood concentration of albumin, entered in g/dL with a default of 3.
Formula and method
AG_corrected = AG_measured + k × (Alb_reference − Alb_measured), where k = 2.5 (mmol/L)/(g/dL) and Alb_reference = 4 g/dL.
- AG_correctedAlbumin-corrected anion gap, in mmol/L.
- AG_measuredMeasured anion gap entered by the user, in mmol/L.
- kFigge approximation coefficient: 2.5 mmol/L of anion gap adjustment per 1 g/dL difference in albumin.
- Alb_referenceThe fixed reference albumin concentration of 4 g/dL.
- Alb_measuredSerum albumin entered by the user, in g/dL.
Subtract the serum albumin from the reference concentration of 4 g/dL, multiply that difference by 2.5, and add the adjustment to the measured anion gap. With the default inputs, AG_corrected = 12 + 2.5 × (4 − 3) = 14.5 mmol/L.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Measured anion gap12 mmol/L
- Serum albumin3 g/dL
Results
- Albumin-corrected anion gap14.5 mmol/L
- NoteEducational estimate for adults; not a diagnosis or treatment recommendation.
How to use the Albumin-Corrected Anion Gap Calculator
- 1Find the measured anion gap and serum albumin from the same blood draw when possible.
- 2Enter the measured anion gap in mmol/L; the default is 12.
- 3Enter serum albumin in g/dL; the default is 3, and values reported in g/L must be divided by 10 before entry.
- 4Calculate the albumin-corrected anion gap; the default inputs produce 14.5 mmol/L.
- 5Read the educational note and discuss clinically relevant results with a qualified healthcare professional.
Reading your result
The “Albumin-corrected anion gap” row displays the estimated gap after adjustment to the reference albumin concentration of 4 g/dL. With the default inputs, this is 14.5 mmol/L, which is 2.5 mmol/L higher than the measured gap of 12 because albumin is below the reference concentration. This value alone does not establish whether an acid–base disorder is present; interpretation depends on the laboratory's anion gap method and reference interval, other laboratory results, and clinical context. The “Note” row states: “Educational estimate for adults; not a diagnosis or treatment recommendation.”
Limitations
This tool uses a linear approximation with a fixed reference albumin of 4 g/dL and does not directly measure unmeasured ions or determine the cause of an abnormal gap. Anion gap values and reference intervals vary by laboratory and by whether potassium is included; the correction does not standardize those differences. Results depend on accurate, appropriately timed inputs in the specified units. Albumin correction cannot replace assessment of pH, bicarbonate, lactate, ketones, kidney function, or other clinically indicated findings, and a normal corrected gap does not rule out an acid–base disorder. This is an educational estimate for adults, not a nutrition assessment or treatment guide.
Common questions
Why does low albumin increase the corrected anion gap?+
Albumin is a major unmeasured anion, so lower albumin tends to reduce the measured anion gap. The correction adds 2.5 mmol/L for each 1 g/dL that albumin is below 4 g/dL, helping account for that effect.
Why do the default inputs produce 14.5 mmol/L?+
With measured anion gap 12 mmol/L and serum albumin 3 g/dL, the albumin shortfall is 4 − 3 = 1 g/dL. The adjustment is 2.5 × 1 = 2.5 mmol/L, giving 12 + 2.5 = 14.5 mmol/L.
Does this calculator include potassium in the anion gap?+
It does not calculate the initial anion gap from electrolytes; it adjusts the value you enter. Check whether your laboratory includes potassium and use a reference interval appropriate to that convention.
What happens if albumin is at or above 4 g/dL?+
At 4 g/dL, the adjustment is zero and the corrected gap equals the measured gap. Above 4 g/dL, the formula subtracts an adjustment because the albumin difference is negative; this remains an approximation rather than a diagnostic finding.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.