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Anion Gap Calculator

Calculate the anion gap from serum electrolytes to help diagnose metabolic acidosis and other acid-base disorders.

Note

Important Health Disclaimer

This calculator provides general health information based on standard medical formulas and WHO guidelines. Results are for informational and educational purposes only and should not be considered as professional medical advice or a personal care recommendation.

For health concerns, medical conditions, fitness plans, or dietary decisions, please consult with qualified healthcare professionals, licensed physicians, registered dietitians, or certified fitness trainers who can evaluate your individual health status and medical history.

Individual health needs vary significantly. These calculations are general estimates and may not be appropriate for everyone, especially those with existing medical conditions, pregnant women, children, or elderly individuals.

Not a substitute for qualified professional guidance

Serum Electrolytes

mEq/L

Normal: 136-145 mEq/L

mEq/L

Normal: 98-106 mEq/L

mEq/L

Normal: 22-26 mEq/L

g/dL

For albumin-corrected AG (Normal: 3.5-5.0 g/dL)

Anion Gap

14.0 mEq/L

High Anion Gap

🧪Standard AG
14.0 mEq/L
📊Corrected AG
14.0 mEq/L
📈Delta Ratio
N/A
✓Normal Range
8-12 mEq/L

Interpretation

Metabolic acidosis with increased anion gap (HAGMA)

Causes of Abnormal Anion Gap

High Anion Gap (MUDPILES)

  • Methanol
  • Uremia
  • Diabetic ketoacidosis
  • Propylene glycol
  • Isoniazid, Iron
  • Lactic acidosis
  • Ethylene glycol
  • Salicylates

Low Anion Gap

  • Hypoalbuminemia
  • Multiple myeloma (paraproteins)
  • Lithium toxicity
  • Bromide ingestion
  • Laboratory error

What Is the Anion Gap?

The anion gap (AG) is a calculated value derived from routine blood electrolyte measurements that helps clinicians identify the cause of metabolic acidosis — a condition where the blood becomes too acidic. In blood, the total number of positively charged ions (cations) must equal the total number of negatively charged ions (anions) to maintain electrical neutrality. The anion gap represents the difference between the measured cations (sodium and sometimes potassium) and the measured anions (chloride and bicarbonate), revealing unmeasured anions — proteins, phosphates, sulfates, and organic acids — that aren't included in routine tests.

A high anion gap metabolic acidosis (HAGMA) indicates the accumulation of unmeasured acids in the blood — most commonly lactic acid, ketoacids (in diabetic ketoacidosis), or toxins like methanol and ethylene glycol. The classic mnemonic MUDPILES (Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates) helps clinicians remember the major causes. A normal anion gap metabolic acidosis (NAGMA) suggests bicarbonate loss through the kidneys or gastrointestinal tract.

The anion gap is an essential tool in emergency medicine, critical care, nephrology, and internal medicine. It's one of the first calculations performed when an arterial or venous blood gas shows acidosis, helping narrow the differential diagnosis within minutes. This calculator computes the standard anion gap, the albumin-corrected gap, and the delta ratio for identifying mixed acid-base disorders.

Anion Gap Formulas

The calculator computes three related values:

Anion Gap Formula

AG = Na⁺ - (Cl⁻ + HCO₃⁻) [Without K⁺] AG = (Na⁺ + K⁺) - (Cl⁻ + HCO₃⁻) [With K⁺]

Where:

  • Na⁺= Serum sodium concentration in mEq/L (normal range: 135-145)
  • Cl⁻= Serum chloride concentration in mEq/L (normal range: 98-107)
  • HCO₃⁻= Serum bicarbonate in mEq/L (normal range: 22-28)
  • K⁺= Serum potassium in mEq/L (optional; normal range: 3.5-5.0)

Albumin-Corrected Anion Gap

A normal or seemingly normal anion gap can be misleading in patients with low albumin (hypoalbuminemia), because albumin is a major unmeasured anion that contributes to the gap. The corrected formula adjusts for this:

Corrected Anion Gap Formula

Corrected AG = AG + 2.5 × (4.0 - Albumin)

Where:

  • AG= Uncorrected anion gap calculated from electrolytes
  • Albumin= Serum albumin in g/dL (normal range: 3.5-5.0)
  • 2.5= Correction factor — each 1 g/dL decrease in albumin below 4.0 increases the anion gap by approximately 2.5 mEq/L

Delta Ratio for Mixed Acid-Base Disorders

The delta ratio (delta gap / delta bicarbonate) helps determine whether a high anion gap metabolic acidosis is pure or mixed with another acid-base disturbance. It compares the increase in anion gap to the decrease in bicarbonate:

Delta RatioInterpretation
Below 1.0Mixed HAGMA and NAGMA — there is more bicarbonate loss than the excess acid alone would explain
1.0 – 2.0Pure high anion gap metabolic acidosis — the bicarbonate drop is proportional to the anion gap increase
Above 2.0HAGMA with concurrent metabolic alkalosis — the bicarbonate is higher than expected, suggesting a co-existing alkalosis

How to Use This Anion Gap Calculator

Enter laboratory values from a recent blood test:

  1. Enter Sodium (Na⁺): From your basic metabolic panel or comprehensive metabolic panel. Normal range: 135-145 mEq/L.
  2. Enter Potassium (K⁺) — optional: Including potassium produces the "K⁺-inclusive" anion gap (normal 12-16 mEq/L), while excluding it gives the standard gap (normal 8-12 mEq/L).
  3. Enter Chloride (Cl⁻): From the same panel. Normal range: 98-107 mEq/L.
  4. Enter Bicarbonate (HCO₃⁻): Often reported as "CO₂" on chemistry panels. Normal range: 22-28 mEq/L.
  5. Enter Albumin: Required for the corrected anion gap. Normal range: 3.5-5.0 g/dL. The corrected gap is especially important in critically ill or malnourished patients where albumin may be low.

Worked Examples

Diabetic Ketoacidosis

Problem:

A patient presents with Na⁺ 132, K⁺ 4.0, Cl⁻ 100, HCO₃⁻ 10, Albumin 4.0. Calculate the anion gap.

Solution Steps:

  1. 1Standard AG (without K⁺): 132 - (100 + 10) = 22 mEq/L
  2. 2Normal range: 8-12 mEq/L — this is significantly elevated
  3. 3Corrected AG: 22 + 2.5 × (4.0 - 4.0) = 22 mEq/L (no correction needed with normal albumin)
  4. 4Delta gap: 22 - 12 = 10; Delta bicarb: 24 - 10 = 14; Delta ratio: 10/14 = 0.71

Result:

Anion gap = 22 mEq/L (High — HAGMA). Delta ratio of 0.71 suggests mixed HAGMA and NAGMA. This pattern is consistent with diabetic ketoacidosis where the high gap is from ketoacids, but the delta ratio below 1.0 suggests some concurrent normal anion gap component, possibly from renal bicarbonate loss.

Normal Anion Gap with Normal Albumin

Problem:

Routine labs show Na⁺ 140, Cl⁻ 104, HCO₃⁻ 25, Albumin 4.2. Any concern?

Solution Steps:

  1. 1AG = 140 - (104 + 25) = 11 mEq/L
  2. 2Normal range: 8-12 mEq/L — within limits
  3. 3Corrected AG: 11 + 2.5 × (4.0 - 4.2) = 11 + 2.5 × (-0.2) = 10.5 mEq/L

Result:

Anion gap = 11 mEq/L (Normal). All values are within reference ranges and the corrected gap is also normal. No evidence of metabolic acidosis.

Tips & Best Practices

  • ✓Always check albumin when interpreting the anion gap — a normal uncorrected gap with low albumin may mask a significant acidosis
  • ✓The delta ratio is only meaningful when the anion gap is elevated — it cannot be calculated in normal-gap states
  • ✓Use the MUDPILES mnemonic for differential diagnosis of high anion gap metabolic acidosis
  • ✓A corrected anion gap above 16 mEq/L with a delta ratio between 1.0-2.0 suggests a pure high anion gap metabolic acidosis

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Frequently Asked Questions

The normal anion gap without potassium is 8-12 mEq/L. With potassium included, the normal range is 12-16 mEq/L. However, modern laboratory analyzers using ion-selective electrodes have shifted reference ranges slightly — many institutions now use 6-12 mEq/L as the normal range without potassium. Always interpret the gap in the context of your laboratory's specific reference range.
Albumin is negatively charged and contributes significantly to the unmeasured anion pool. In hypoalbuminemia, the decrease in negatively charged albumin narrows the anion gap, potentially masking the presence of unmeasured acids that would otherwise elevate it. A patient with lactic acidosis and low albumin may have a 'normal' appearing anion gap of 11 when the corrected gap reveals 18. This is why albumin correction is essential in malnourished, critically ill, or cirrhotic patients.
A low or negative anion gap is unusual and can indicate: 1) Hypoalbuminemia (most common), 2) Multiple myeloma where positively charged paraproteins narrow the gap, 3) Laboratory error (including delayed processing causing bicarbonate to rise artificially), 4) Lithium or bromide toxicity (measured as chloride by some analyzers, falsely elevating apparent Cl⁻). A low gap should prompt albumin measurement and consideration of paraprotein disorders.
Most clinical practice in the United States calculates the anion gap without potassium because potassium's contribution is relatively small (normal range only shifts by approximately 4 mEq/L). Including potassium gives a slightly wider normal range (12-16 vs 8-12 mEq/L). Both methods are valid — the key is consistency and awareness of which reference range applies. European guidelines more commonly include potassium.

Sources & References

Last updated: 2026-06-06

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Sources

  • •World Health Organization (WHO) — Global health metrics, disease classification, and nutritional standards. who.int
  • •Centers for Disease Control and Prevention (CDC) — Health statistics, BMI guidelines, and disease prevention data. cdc.gov
  • •National Institutes of Health (NIH) — Medical research, clinical guidelines, and health calculators. nih.gov
  • •Mayo Clinic — Clinical health information, disease reference, and wellness guidance. mayoclinic.org

For a complete list of all references used across the site, visit our full sources page.

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Editorial Note

MyCalcBuddy Editorial Team

This page is maintained as an educational calculator reference.

Source

Formula Source: WHO Health Metrics Standards

by World Health Organization

UpdatedLast reviewed: May 2026
CheckedFormula checks are based on standard references and internal QA review.