How do you calculate the anion gap?

Subtract chloride plus bicarbonate from sodium: AG = Na⁺ − (Cl⁻ + HCO₃⁻). Enter sodium, chloride and bicarbonate/total CO₂ from the same laboratory time point where possible. The calculator does not apply a universal normal/high cutoff.

What is a normal anion gap?

Use the reporting laboratory's own reference interval rather than one universal range. Reference intervals vary with analyser method, population and whether potassium is included. For clinical meaning, use the dedicated anion-gap interpretation Guide.

Why can albumin change the anion gap calculation?

Albumin is an important unmeasured anion, so low albumin can lower the observed gap. MedMaths can show an optional albumin-adjusted estimate alongside the standard gap. Albumin adjustment is an estimate, not a universal laboratory standard, and its clinical utility is debated.

How is the albumin-adjusted anion gap calculated?

MedMaths uses adjusted AG = AG + 2.5 × (4.0 − albumin in g/dL) as a common convention. If albumin is entered in g/L, MedMaths converts it to g/dL before applying the adjustment. Keep the standard anion gap and the measured albumin visible rather than replacing them with the adjusted estimate.

Does this calculator include potassium?

No. MedMaths uses the potassium-free equation AG = Na⁺ − (Cl⁻ + HCO₃⁻). Some laboratories use a potassium-inclusive equation. The reference interval must match the equation convention used by the reporting laboratory.

Why can different anion-gap calculators give different numbers or ranges?

Equation convention, laboratory measurement methods and albumin-adjustment choices can differ. Check whether potassium is included and whether an albumin adjustment has been applied. Use the reporting laboratory's method and reference interval for interpretation.

Can the anion gap diagnose DKA or show that DKA has resolved?

No. Current DKA guidance prioritises ketosis and acid-base criteria; the anion gap is an adjunct rather than a first-line diagnostic or resolution criterion when direct ketone testing is available. The 2026 ADA criteria require diabetes/hyperglycaemia, ketosis and metabolic acidosis; anion gap is not one of the required diagnostic criteria. The 2024 international consensus recommends direct blood beta-hydroxybutyrate for diagnosis and monitoring and warns that mixed disorders or treatment-related hyperchloraemic acidosis can make the gap misleading. Do not use gap normalisation by itself to declare DKA resolved.

Should sodium, chloride, bicarbonate and albumin come from the same sample?

Ideally use values from the same clinical time point, especially when the patient or treatment is changing quickly. Mixing values from different time points can create an arithmetic result that did not exist in one sample. Check the source values before interpreting an unexpected result.

Anion Gap Calculator

Lab corrections

What is the anion gap?

Enter sodium, chloride and bicarbonate/total CO₂. Add albumin only if you want the optional albumin-adjusted estimate.

Sodium (Na⁺)*mmol/L / mEq/L

Enter the measured serum sodium. For Na⁺, mmol/L and mEq/L are numerically equivalent.

Chloride (Cl⁻)*mmol/L / mEq/L

Enter the measured serum chloride. For Cl⁻, mmol/L and mEq/L are numerically equivalent.

Bicarbonate (HCO₃⁻)*mmol/L / mEq/L

Use the chemistry-panel bicarbonate/total CO₂ term used by your laboratory. Avoid mixing chemistry and blood-gas values without clinical context.

Albumin correction

Choose whether to calculate the standard anion gap alone or also show an optional albumin-adjusted estimate.

Use values from the same laboratory time point

The anion gap is calculated from measured electrolytes. If albumin correction is selected, use an albumin result from the same clinical context whenever possible.

Simple answer

How do you calculate the standard anion gap?

Subtract chloride plus bicarbonate from sodium using the potassium-free equation used by this calculator.

Example: Na 140, Cl 104 and HCO₃ 24 gives 140 − (104 + 24) = 12 mmol/L.

This is the standard potassium-free anion gap calculated by MedMaths.

Simple answer

How do you calculate the optional albumin-adjusted anion gap?

When albumin adjustment is selected, MedMaths applies a common albumin-correction estimate to the standard anion gap.

Example: AG 12 with albumin 2.0 g/dL gives 12 + 2.5 × (4.0 − 2.0) = 17 mmol/L.

Albumin adjustment is an estimate, not a universal laboratory standard. Keep the standard anion gap and measured albumin visible.

Use the laboratory's own reference interval

Anion-gap reference intervals vary with laboratory methods and equation conventions. Do not treat one universal cutoff as a substitute for the local laboratory range or full acid-base assessment.

Clinical use and safety

When to use this calculator — and its limits

The arithmetic can be correct while the clinical decision is still wrong. These boundaries show what the calculator can and cannot establish.

When to use

Use when you need the standard potassium-free serum/plasma anion gap from sodium, chloride and bicarbonate/total CO₂ values obtained from the same clinical time point where possible.
Compare the calculated gap with the reference interval used by the reporting laboratory and the same equation convention; a potassium-inclusive equation produces a different numerical result.
Use the optional albumin-adjusted value only as a secondary estimate when the clinical source or local practice specifically uses an albumin correction.

Key limitations

There is no universal normal anion-gap cutoff. Reference intervals depend on analyser method, laboratory calibration, population, and whether potassium is included; contemporary studies continue to show method-dependent ranges.
The anion gap is a calculated clue within acid-base assessment, not a direct measurement of unmeasured acids. A normal gap does not exclude clinically important acidosis or a mixed acid-base disorder. A normal anion gap also does not exclude elevated lactate; measure lactate directly when clinically indicated.
Hypoalbuminaemia lowers the observed gap. Figge and colleagues quantified an albumin effect, but albumin-adjustment formulas remain debated; a 2022 review concluded that routine correction has no proven clinical advantage and may increase misinterpretation or error.
The optional MedMaths albumin correction uses 2.5 mmol/L per 1 g/dL albumin difference with a 4.0 g/dL reference. That reference baseline is not a universal laboratory standard.
Unexpected low or negative gaps should first prompt a check of the original values and laboratory process when appropriate. Hypoalbuminaemia, lithium or other unmeasured cations, positively charged monoclonal proteins, and some chloride or sodium measurement interferences can also lower the calculated gap.
In suspected or treated diabetic ketoacidosis, use current DKA criteria and direct ketone measurement where available. The anion gap is not recommended as a first-line diagnostic or resolution criterion, and gap normalisation alone should not be used to declare DKA resolved.

What MedMaths does not decide

Whether metabolic acidosis or another acid-base disorder is present; pH, bicarbonate/total CO₂, blood-gas findings and the clinical context still matter.
The cause of an increased, normal or low anion gap, including whether lactate, ketones, renal acids, toxins or another process is responsible; a normal gap does not rule out hyperlactataemia.
Whether albumin correction should be used by a particular laboratory or clinical service.
Treatment, toxicology management, fluid therapy, bicarbonate therapy or the need for direct lactate, beta-hydroxybutyrate, toxic alcohol or other testing.
Whether diabetic ketoacidosis is present or resolved; current DKA diagnosis and monitoring use diabetes/hyperglycaemia, ketosis and acid-base criteria rather than the anion gap alone.

Evidence and method checks

Serum anion gap revisited: a verified reference interval for contemporary use — Internal Medicine Journal / PubMed
Anion gap and hypoalbuminemia — Critical Care Medicine / PubMed
Anion gap physiology and faults of the correction formula — American Journal of Health-System Pharmacy / PubMed
Harmonising Reference Intervals for Three Calculated Parameters used in Clinical Chemistry — Clinical Biochemist Reviews / PubMed Central
Hyperglycemic Crises in Adults With Diabetes: A Consensus Report — ADA / Diabetes Care / PubMed Central
Diabetes Care in the Hospital: Standards of Care in Diabetes—2026 — American Diabetes Association
Evaluating a low anion gap: A practical approach — Cleveland Clinic Journal of Medicine
Validity of anion gap as a screening tool for hyperlactatemia: systematic review and meta-analysis — BMC Research Notes / PubMed Central
Albumin, Serum — reference values in g/dL — Mayo Clinic Laboratories
Albumin — reference interval reported in g/L — Royal College of Pathologists of Australasia

Formula logic and known-value examples are checked as part of the MedMaths review process.

See how MedMaths checks calculator methods →

Calculate here

Use this page for the potassium-free anion-gap arithmetic and the optional albumin-adjusted estimate. Compare the result with the reporting laboratory's own reference interval.

Need to interpret the result?

High-gap causes, GOLDMARK, normal-gap acidosis, low/negative gaps and broader clinical interpretation belong in the dedicated Guide.

Read the anion gap interpretation Guide →

Formula, examples and common questions

Review the exact equation convention, albumin-adjustment evidence, two worked examples, common input mistakes and focused FAQs.

Anion gap formula and conventions

Standard potassium-free anion gap

In simple words

This is the equation used by MedMaths. For sodium, chloride and bicarbonate, mmol/L and mEq/L are numerically equivalent because these ions are monovalent.

Na⁺: = measured serum/plasma sodium
Cl⁻: = measured serum/plasma chloride
HCO₃⁻: = the bicarbonate/total CO₂ term used by the reporting laboratory
AG: = calculated potassium-free anion gap

Optional albumin-adjusted estimate

Adjusted AG = AG + 2.5 × (4.0 − albumin g/dL)

James J. Figge and colleagues quantified an albumin effect of about 2.5 mEq/L per 1 g/dL. MedMaths uses a common 4.0 g/dL reference baseline, but that baseline and routine use of correction are not universal standards.

Potassium-inclusive convention

AG = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻)

Some laboratories and references include potassium. That produces a different number, so the reference interval must match the equation convention.

Albumin adjustment is optional: the 1998 Figge study supports the albumin relationship, while a 2022 peer-reviewed review argued that routine correction offers no proven clinical advantage and may increase error. Keep the standard gap and measured albumin visible.

Worked examples

Two examples cover the standard calculation and the optional albumin-adjusted estimate.

Example 1 — standard potassium-free anion gap

Na = 140, Cl = 104, HCO₃ = 24 mmol/L
AG = 140 − (104 + 24)
AG = 12 mmol/L
Compare 12 with the reference interval from the same laboratory and equation convention.

Example 2 — optional albumin adjustment

Standard AG = 12 mmol/L, albumin = 2.0 g/dL
Adjustment = 2.5 × (4.0 − 2.0) = 5
Albumin-adjusted estimate = 17 mmol/L
Keep the standard AG of 12 and measured albumin of 2.0 g/dL visible alongside the estimate.

Common anion-gap calculation mistakes

Using a universal normal range

Reference intervals differ by laboratory, analyser and equation convention. Use the interval reported with the patient's results.

Mixing potassium conventions

MedMaths excludes potassium. Do not compare a potassium-free result with a potassium-inclusive reference interval.

Mixing chemistry and blood-gas values

Chemistry-panel total CO₂ and blood-gas calculated bicarbonate are not automatically interchangeable. Use the convention your laboratory uses for its anion gap.

Mixing different time points

Sodium, chloride, bicarbonate/total CO₂ and albumin can change during treatment. Use contemporaneous values where possible.

Treating the adjusted value as a measured test

Albumin-adjusted AG is a calculated estimate. Keep the standard AG and actual albumin visible.

Entering albumin in the wrong unit

Albumin can be reported as g/dL or g/L, a 10-fold scale difference. Select the unit shown on the laboratory report; MedMaths will warn rather than silently guess when the value strongly resembles the other unit scale.

Frequently Asked Questions

Calculation method

The potassium-free anion gap is standard clinical arithmetic: sodium minus chloride plus bicarbonate. MedMaths does not attribute that arithmetic to a single inventor. The optional albumin adjustment uses the widely cited 2.5 mmol/L per 1 g/dL albumin relationship quantified by Figge and colleagues in 1998, with a common 4.0 g/dL reference baseline. The reporting laboratory's own anion-gap convention and reference interval remain authoritative.

Supporting references

Clinical use of the anion gap — Medicine / PubMed
Anion gap and hypoalbuminemia — Critical Care Medicine / PubMed
The serum anion gap. Has the reference interval really fallen? — Archives of Pathology & Laboratory Medicine / PubMed
Serum anion gap revisited: a verified reference interval for contemporary use — Internal Medicine Journal / PubMed
Anion gap physiology and faults of the correction formula — American Journal of Health-System Pharmacy / PubMed
Approach to Patients With High Anion Gap Metabolic Acidosis: Core Curriculum 2021 — American Journal of Kidney Diseases / PubMed
GOLD MARK: an anion gap mnemonic for the 21st century — Lancet / PubMed

Safety and quality guidance

Hyperglycemic Crises in Adults With Diabetes: A Consensus Report — ADA / Diabetes Care / PubMed Central
Diabetes Care in the Hospital: Standards of Care in Diabetes—2026 — American Diabetes Association
Evaluating a low anion gap: A practical approach — Cleveland Clinic Journal of Medicine
Validity of anion gap as a screening tool for hyperlactatemia: systematic review and meta-analysis — BMC Research Notes / PubMed Central

Continue calculating

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Calculate serum osmolality from sodium, glucose and urea, with optional osmol gap calculation.

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References and sources

Open the source material for anion-gap interpretation, albumin adjustment, unit handling, DKA and key safety limitations.

Albumin adjustment evidence

Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807–1810.

PubMed PMID 9824071 James J. Figge researcher profile

Anion gap framework

Emmett M, Narins RG. Clinical use of the anion gap. Medicine. 1977;56(1):38–54.

PubMed PMID 401925

Laboratory-specific reference intervals

Roberts WL, Johnson RD. The serum anion gap. Has the reference interval really fallen? Arch Pathol Lab Med. 1997;121(6):568–572.

PubMed PMID 9199620

Contemporary reference interval study

Chionh CYC, et al. Serum anion gap revisited: a verified reference interval for contemporary use. Intern Med J. 2022;52(9):1531–1537.

PubMed PMID 34028972

Total CO₂ and blood-gas bicarbonate

Goldwasser P, Manjappa NG, Luhrs CA, Barth RH. Pseudohypobicarbonatemia caused by an endogenous assay interferent: a new entity. Am J Kidney Dis. 2011.

PubMed PMID 21849226

Albumin unit scales

Albumin is commonly reported in g/dL in U.S. laboratory material and in g/L in Australian laboratory material. The units differ by a factor of 10, so MedMaths requires the selected unit to match the laboratory report and does not silently infer a conversion.

Mayo Clinic Laboratories — g/dL reference values RCPA — g/L reference interval

Current DKA diagnostic and monitoring guidance

Umpierrez GE, et al. Hyperglycemic Crises in Adults With Diabetes: A Consensus Report. Diabetes Care. 2024;47(8):1257–1275. doi:10.2337/dci24-0032.

Open-access consensus report PubMed PMID 39052901

ADA Standards of Care in Diabetes—2026

American Diabetes Association Professional Practice Committee. Diabetes Care in the Hospital: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1).

ADA 2026 hospital-care standard

Low or negative anion gap

Haber LA, Dhaliwal G, Lo L, Rizzuto G. Evaluating a low anion gap: A practical approach. Cleve Clin J Med. 2023;90(10):619–623. doi:10.3949/ccjm.90a.23035.

Cleveland Clinic Journal of Medicine

High-gap metabolic acidosis and GOLDMARK

Fenves AZ, Emmett M. Approach to Patients With High Anion Gap Metabolic Acidosis: Core Curriculum 2021. Am J Kidney Dis. 2021;78(4):590–600. Mehta AN, Emmett JB, Emmett M. GOLD MARK: an anion gap mnemonic for the 21st century. Lancet. 2008;372:892.

AJKD Core Curriculum PMID 34400023 GOLDMARK PMID 18790311

Anion gap is not a substitute for lactate

Glasmacher SA, Stones W. A systematic review and diagnostic test accuracy meta-analysis of the validity of anion gap as a screening tool for hyperlactatemia. BMC Res Notes. 2017;10:556. doi:10.1186/s13104-017-2853-9.

Open-access systematic review

Anion Gap Calculator

Lab corrections

What is the anion gap?

Enter sodium, chloride and bicarbonate/total CO₂. Add albumin only if you want the optional albumin-adjusted estimate.

Sodium (Na⁺)*mmol/L / mEq/L

Enter the measured serum sodium. For Na⁺, mmol/L and mEq/L are numerically equivalent.

Chloride (Cl⁻)*mmol/L / mEq/L

Enter the measured serum chloride. For Cl⁻, mmol/L and mEq/L are numerically equivalent.

Bicarbonate (HCO₃⁻)*mmol/L / mEq/L

Use the chemistry-panel bicarbonate/total CO₂ term used by your laboratory. Avoid mixing chemistry and blood-gas values without clinical context.

Albumin correction

Choose whether to calculate the standard anion gap alone or also show an optional albumin-adjusted estimate.

Use values from the same laboratory time point

The anion gap is calculated from measured electrolytes. If albumin correction is selected, use an albumin result from the same clinical context whenever possible.

Simple answer

How do you calculate the standard anion gap?

Subtract chloride plus bicarbonate from sodium using the potassium-free equation used by this calculator.

Example: Na 140, Cl 104 and HCO₃ 24 gives 140 − (104 + 24) = 12 mmol/L.

This is the standard potassium-free anion gap calculated by MedMaths.

Simple answer

How do you calculate the optional albumin-adjusted anion gap?

When albumin adjustment is selected, MedMaths applies a common albumin-correction estimate to the standard anion gap.

Example: AG 12 with albumin 2.0 g/dL gives 12 + 2.5 × (4.0 − 2.0) = 17 mmol/L.

Albumin adjustment is an estimate, not a universal laboratory standard. Keep the standard anion gap and measured albumin visible.

Use the laboratory's own reference interval

Anion-gap reference intervals vary with laboratory methods and equation conventions. Do not treat one universal cutoff as a substitute for the local laboratory range or full acid-base assessment.

Clinical use and safety

When to use this calculator — and its limits

The arithmetic can be correct while the clinical decision is still wrong. These boundaries show what the calculator can and cannot establish.

When to use

Use when you need the standard potassium-free serum/plasma anion gap from sodium, chloride and bicarbonate/total CO₂ values obtained from the same clinical time point where possible.
Compare the calculated gap with the reference interval used by the reporting laboratory and the same equation convention; a potassium-inclusive equation produces a different numerical result.
Use the optional albumin-adjusted value only as a secondary estimate when the clinical source or local practice specifically uses an albumin correction.

Key limitations

There is no universal normal anion-gap cutoff. Reference intervals depend on analyser method, laboratory calibration, population, and whether potassium is included; contemporary studies continue to show method-dependent ranges.
The anion gap is a calculated clue within acid-base assessment, not a direct measurement of unmeasured acids. A normal gap does not exclude clinically important acidosis or a mixed acid-base disorder. A normal anion gap also does not exclude elevated lactate; measure lactate directly when clinically indicated.
Hypoalbuminaemia lowers the observed gap. Figge and colleagues quantified an albumin effect, but albumin-adjustment formulas remain debated; a 2022 review concluded that routine correction has no proven clinical advantage and may increase misinterpretation or error.
The optional MedMaths albumin correction uses 2.5 mmol/L per 1 g/dL albumin difference with a 4.0 g/dL reference. That reference baseline is not a universal laboratory standard.
Unexpected low or negative gaps should first prompt a check of the original values and laboratory process when appropriate. Hypoalbuminaemia, lithium or other unmeasured cations, positively charged monoclonal proteins, and some chloride or sodium measurement interferences can also lower the calculated gap.
In suspected or treated diabetic ketoacidosis, use current DKA criteria and direct ketone measurement where available. The anion gap is not recommended as a first-line diagnostic or resolution criterion, and gap normalisation alone should not be used to declare DKA resolved.

What MedMaths does not decide

Whether metabolic acidosis or another acid-base disorder is present; pH, bicarbonate/total CO₂, blood-gas findings and the clinical context still matter.
The cause of an increased, normal or low anion gap, including whether lactate, ketones, renal acids, toxins or another process is responsible; a normal gap does not rule out hyperlactataemia.
Whether albumin correction should be used by a particular laboratory or clinical service.
Treatment, toxicology management, fluid therapy, bicarbonate therapy or the need for direct lactate, beta-hydroxybutyrate, toxic alcohol or other testing.
Whether diabetic ketoacidosis is present or resolved; current DKA diagnosis and monitoring use diabetes/hyperglycaemia, ketosis and acid-base criteria rather than the anion gap alone.

Evidence and method checks

Serum anion gap revisited: a verified reference interval for contemporary use — Internal Medicine Journal / PubMed
Anion gap and hypoalbuminemia — Critical Care Medicine / PubMed
Anion gap physiology and faults of the correction formula — American Journal of Health-System Pharmacy / PubMed
Harmonising Reference Intervals for Three Calculated Parameters used in Clinical Chemistry — Clinical Biochemist Reviews / PubMed Central
Hyperglycemic Crises in Adults With Diabetes: A Consensus Report — ADA / Diabetes Care / PubMed Central
Diabetes Care in the Hospital: Standards of Care in Diabetes—2026 — American Diabetes Association
Evaluating a low anion gap: A practical approach — Cleveland Clinic Journal of Medicine
Validity of anion gap as a screening tool for hyperlactatemia: systematic review and meta-analysis — BMC Research Notes / PubMed Central
Albumin, Serum — reference values in g/dL — Mayo Clinic Laboratories
Albumin — reference interval reported in g/L — Royal College of Pathologists of Australasia

Formula logic and known-value examples are checked as part of the MedMaths review process.

See how MedMaths checks calculator methods →

Calculate here

Use this page for the potassium-free anion-gap arithmetic and the optional albumin-adjusted estimate. Compare the result with the reporting laboratory's own reference interval.

Need to interpret the result?

High-gap causes, GOLDMARK, normal-gap acidosis, low/negative gaps and broader clinical interpretation belong in the dedicated Guide.

Read the anion gap interpretation Guide →

Formula, examples and common questions

Review the exact equation convention, albumin-adjustment evidence, two worked examples, common input mistakes and focused FAQs.

Anion gap formula and conventions

Standard potassium-free anion gap

In simple words

This is the equation used by MedMaths. For sodium, chloride and bicarbonate, mmol/L and mEq/L are numerically equivalent because these ions are monovalent.

Na⁺: = measured serum/plasma sodium
Cl⁻: = measured serum/plasma chloride
HCO₃⁻: = the bicarbonate/total CO₂ term used by the reporting laboratory
AG: = calculated potassium-free anion gap

Optional albumin-adjusted estimate

Adjusted AG = AG + 2.5 × (4.0 − albumin g/dL)

Potassium-inclusive convention

AG = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻)

Some laboratories and references include potassium. That produces a different number, so the reference interval must match the equation convention.

Worked examples

Two examples cover the standard calculation and the optional albumin-adjusted estimate.

Example 1 — standard potassium-free anion gap

Na = 140, Cl = 104, HCO₃ = 24 mmol/L
AG = 140 − (104 + 24)
AG = 12 mmol/L
Compare 12 with the reference interval from the same laboratory and equation convention.

Example 2 — optional albumin adjustment

Standard AG = 12 mmol/L, albumin = 2.0 g/dL
Adjustment = 2.5 × (4.0 − 2.0) = 5
Albumin-adjusted estimate = 17 mmol/L
Keep the standard AG of 12 and measured albumin of 2.0 g/dL visible alongside the estimate.

Common anion-gap calculation mistakes

Using a universal normal range

Reference intervals differ by laboratory, analyser and equation convention. Use the interval reported with the patient's results.

Mixing potassium conventions

MedMaths excludes potassium. Do not compare a potassium-free result with a potassium-inclusive reference interval.

Mixing chemistry and blood-gas values

Chemistry-panel total CO₂ and blood-gas calculated bicarbonate are not automatically interchangeable. Use the convention your laboratory uses for its anion gap.

Mixing different time points

Sodium, chloride, bicarbonate/total CO₂ and albumin can change during treatment. Use contemporaneous values where possible.

Treating the adjusted value as a measured test

Albumin-adjusted AG is a calculated estimate. Keep the standard AG and actual albumin visible.

Entering albumin in the wrong unit

Frequently Asked Questions

Calculation method

Supporting references

Clinical use of the anion gap — Medicine / PubMed
Anion gap and hypoalbuminemia — Critical Care Medicine / PubMed
The serum anion gap. Has the reference interval really fallen? — Archives of Pathology & Laboratory Medicine / PubMed
Serum anion gap revisited: a verified reference interval for contemporary use — Internal Medicine Journal / PubMed
Anion gap physiology and faults of the correction formula — American Journal of Health-System Pharmacy / PubMed
Approach to Patients With High Anion Gap Metabolic Acidosis: Core Curriculum 2021 — American Journal of Kidney Diseases / PubMed
GOLD MARK: an anion gap mnemonic for the 21st century — Lancet / PubMed

Safety and quality guidance

Hyperglycemic Crises in Adults With Diabetes: A Consensus Report — ADA / Diabetes Care / PubMed Central
Diabetes Care in the Hospital: Standards of Care in Diabetes—2026 — American Diabetes Association
Evaluating a low anion gap: A practical approach — Cleveland Clinic Journal of Medicine
Validity of anion gap as a screening tool for hyperlactatemia: systematic review and meta-analysis — BMC Research Notes / PubMed Central

Continue calculating

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Use these calculators when interpreting acid-base status or related laboratory results.

Corrected Calcium Calculator

Calculate the commonly used simplified albumin-adjusted calcium estimate with current evidence limitations.

Open calculator

eGFR Calculator (CKD-EPI 2021)

Calculate the modern race-free 2021 CKD-EPI eGFR, with optional cystatin C and BSA adjustment.

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Calculate adult Cockcroft-Gault CrCl when a medicine label, protocol or exam specifically requires this method.

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mg/kg to mL Dose Calculator

Calculate mg/kg per-dose or per-day orders using kg or lb, divided doses, and liquid concentration.

Open calculator

Corrected Sodium Calculator

Adjust serum sodium for hyperglycaemia using the Katz or Hillier correction formula.

Open calculator

Serum Osmolality Calculator

Calculate serum osmolality from sodium, glucose and urea, with optional osmol gap calculation.

Open calculator

References and sources

Open the source material for anion-gap interpretation, albumin adjustment, unit handling, DKA and key safety limitations.

Albumin adjustment evidence

Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807–1810.

PubMed PMID 9824071 James J. Figge researcher profile

Anion gap framework

Emmett M, Narins RG. Clinical use of the anion gap. Medicine. 1977;56(1):38–54.

PubMed PMID 401925

Laboratory-specific reference intervals

Roberts WL, Johnson RD. The serum anion gap. Has the reference interval really fallen? Arch Pathol Lab Med. 1997;121(6):568–572.

PubMed PMID 9199620

Contemporary reference interval study

Chionh CYC, et al. Serum anion gap revisited: a verified reference interval for contemporary use. Intern Med J. 2022;52(9):1531–1537.

PubMed PMID 34028972

Total CO₂ and blood-gas bicarbonate

Goldwasser P, Manjappa NG, Luhrs CA, Barth RH. Pseudohypobicarbonatemia caused by an endogenous assay interferent: a new entity. Am J Kidney Dis. 2011.

PubMed PMID 21849226

Albumin unit scales

Mayo Clinic Laboratories — g/dL reference values RCPA — g/L reference interval

Current DKA diagnostic and monitoring guidance

Umpierrez GE, et al. Hyperglycemic Crises in Adults With Diabetes: A Consensus Report. Diabetes Care. 2024;47(8):1257–1275. doi:10.2337/dci24-0032.

Open-access consensus report PubMed PMID 39052901

ADA Standards of Care in Diabetes—2026

American Diabetes Association Professional Practice Committee. Diabetes Care in the Hospital: Standards of Care in Diabetes—2026. Diabetes Care. 2026;49(Suppl 1).

ADA 2026 hospital-care standard

Low or negative anion gap

Haber LA, Dhaliwal G, Lo L, Rizzuto G. Evaluating a low anion gap: A practical approach. Cleve Clin J Med. 2023;90(10):619–623. doi:10.3949/ccjm.90a.23035.

Cleveland Clinic Journal of Medicine

High-gap metabolic acidosis and GOLDMARK

AJKD Core Curriculum PMID 34400023 GOLDMARK PMID 18790311

Anion gap is not a substitute for lactate

Open-access systematic review

Anion Gap Calculator

How do you calculate the standard anion gap?

How do you calculate the optional albumin-adjusted anion gap?

Use the laboratory's own reference interval

When to use this calculator — and its limits

When to use

Key limitations

What MedMaths does not decide

Evidence and method checks

Calculate here

Need to interpret the result?

Formula, examples and common questions

Anion gap formula and conventions

Standard potassium-free anion gap

Worked examples

Example 1 — standard potassium-free anion gap

Example 2 — optional albumin adjustment

Common anion-gap calculation mistakes

Using a universal normal range

Mixing potassium conventions

Mixing chemistry and blood-gas values

Mixing different time points

Treating the adjusted value as a measured test

Entering albumin in the wrong unit

Frequently Asked Questions

QWhat is the anion gap?

QHow do you calculate the anion gap?

QWhat is a normal anion gap?

QWhy can albumin change the anion gap calculation?

QHow is the albumin-adjusted anion gap calculated?

QDoes this calculator include potassium?

QWhy can different anion-gap calculators give different numbers or ranges?

QCan the anion gap diagnose DKA or show that DKA has resolved?

QShould sodium, chloride, bicarbonate and albumin come from the same sample?

Calculation method

Related lab and renal calculators

Corrected Calcium Calculator

eGFR Calculator (CKD-EPI 2021)

Creatinine Clearance Calculator

mg/kg to mL Dose Calculator

Corrected Sodium Calculator

Serum Osmolality Calculator

References and sources

Anion Gap Calculator

How do you calculate the standard anion gap?

How do you calculate the optional albumin-adjusted anion gap?

Use the laboratory's own reference interval

When to use this calculator — and its limits

When to use

Key limitations

What MedMaths does not decide

Evidence and method checks

Calculate here

Need to interpret the result?

Formula, examples and common questions

Anion gap formula and conventions

Standard potassium-free anion gap

Worked examples

Example 1 — standard potassium-free anion gap

Example 2 — optional albumin adjustment

Common anion-gap calculation mistakes

Using a universal normal range

Mixing potassium conventions

Mixing chemistry and blood-gas values

Mixing different time points

Treating the adjusted value as a measured test

Entering albumin in the wrong unit

Frequently Asked Questions

QWhat is the anion gap?

QHow do you calculate the anion gap?

QWhat is a normal anion gap?

QWhy can albumin change the anion gap calculation?

QHow is the albumin-adjusted anion gap calculated?

QDoes this calculator include potassium?

QWhy can different anion-gap calculators give different numbers or ranges?

QCan the anion gap diagnose DKA or show that DKA has resolved?

QShould sodium, chloride, bicarbonate and albumin come from the same sample?

Calculation method

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Corrected Calcium Calculator