Serum sodium from BMP/CMP
Enter sodium (100-180).
Serum chloride from BMP/CMP
Enter chloride (60-140).
From BMP or ABG
Enter HCO3 (2-50).
For albumin-corrected AG (normal = 4.0 g/dL)
From ABG — for Winter's formula check
Anion Gap
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⚠️ Medical Disclaimer: Full acid-base interpretation requires pH, pCO2, clinical context, and physician assessment. This calculator provides the mathematical components only. All clinical decisions must be made by a licensed healthcare provider.
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Sources & Methodology
Anion gap and delta ratio formulas per standard clinical chemistry and Harrison's Principles of Internal Medicine.
Harrison's Principles of Internal Medicine, 21st Ed.
Standard reference for acid-base disorders, anion gap calculation, and delta ratio interpretation.
Emmett M & Narins RG — NEJM: Clinical Use of the Anion Gap
Foundational review of anion gap methodology and albumin correction. nejm.org
Kamel KS et al. — Approach to Acid-Base Disorders (NEJM)
Systematic approach to acid-base interpretation including delta ratio and mixed disorder detection.
Anion Gap = Na - (Cl + HCO3) [Normal: 8-12 mEq/L]
Corrected AG = AG + 2.5 x (4.0 - Albumin g/dL)
Delta Ratio = (AG - 12) / (24 - HCO3)
Winter's formula: Expected pCO2 = 1.5 x HCO3 + 8 (+/-2)
Corrected AG = AG + 2.5 x (4.0 - Albumin g/dL)
Delta Ratio = (AG - 12) / (24 - HCO3)
Winter's formula: Expected pCO2 = 1.5 x HCO3 + 8 (+/-2)
AG = Na - (Cl + HCO3)
Example: Na 140, Cl 104, HCO3 16.
AG = 140 - (104 + 16) = 20 mEq/L (elevated — HAGMA).
Delta ratio = (20-12) / (24-16) = 8/8 = 1.0 (pure HAGMA).
AG = 140 - (104 + 16) = 20 mEq/L (elevated — HAGMA).
Delta ratio = (20-12) / (24-16) = 8/8 = 1.0 (pure HAGMA).
Last reviewed: April 2026
How Are Anion Gap and Delta Ratio Used in Acid-Base Interpretation?
The anion gap (AG) is the difference between the major measured cation (sodium) and the major measured anions (chloride + bicarbonate). This gap represents unmeasured anions — mainly albumin, phosphate, sulfate, and organic acids. An elevated AG indicates the presence of pathological unmeasured anions (lactate, ketoacids, toxins) causing metabolic acidosis.
The delta ratio (delta-delta) compares how much the AG has risen against how much the bicarbonate has fallen. In a pure HAGMA, every 1 mEq/L rise in AG should correspond to approximately 1 mEq/L fall in HCO3. Deviations from this 1:1 relationship reveal mixed disorders hidden within the primary diagnosis.
Delta Ratio Interpretation
| Delta Ratio | Interpretation | Clinical Example |
|---|---|---|
| Below 0.4 | Pure NAGMA or mixed HAGMA + NAGMA | Severe diarrhea, RTA |
| 0.4-1.0 | Mixed HAGMA + NAGMA | DKA with diarrhea, early lactic acidosis |
| 1.0-2.0 | Pure HAGMA | Classic DKA, lactic acidosis |
| Above 2.0 | HAGMA + concurrent metabolic alkalosis | DKA with vomiting, DKA with diuretics |
HAGMA Causes — MUDPILES / GOLDMARK
MUDPILES: Methanol, Uremia, DKA, Propylene glycol/Paraldehyde, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates.
GOLDMARK (more current): Glycols, Oxoproline (acetaminophen chronic toxicity), L-lactate, D-lactate (gut bacteria), Methanol, Aspirin, Renal failure, Ketoacidosis.
💡 Hypoalbuminemia — The Hidden HAGMA Trap: Albumin contributes approximately 2.5 mEq/L to the anion gap per g/dL. A critically ill patient with albumin 2.0 g/dL has a baseline AG correction of +5 mEq/L. If this patient's measured AG is 12 (seemingly normal), their corrected AG is 17 — indicating true HAGMA that would be missed without albumin correction. Always correct the AG in hypoalbuminemic patients.
Frequently Asked Questions
AG = Na - (Cl + HCO3). Represents unmeasured anions. Normal: 8-12 mEq/L. Elevated AG indicates unmeasured anions (lactate, ketoacids, toxins) causing metabolic acidosis.
MUDPILES: Methanol, Uremia, DKA, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates. Also GOLDMARK: Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis.
AG = Na - (Cl + HCO3). Example: Na 140, Cl 104, HCO3 16: AG = 140 - 120 = 20 mEq/L (elevated, HAGMA).
Corrected AG = Measured AG + 2.5 x (4.0 - Albumin). Albumin is a major unmeasured anion. Low albumin falsely lowers AG — correcting reveals hidden HAGMA in hypoalbuminemic patients.
Delta ratio = (AG - 12) / (24 - HCO3). Compares AG rise to HCO3 fall. Below 0.4: pure NAGMA. 0.4-1.0: mixed HAGMA + NAGMA. 1.0-2.0: pure HAGMA. Above 2.0: HAGMA + metabolic alkalosis.
HAGMA plus concurrent metabolic alkalosis. HCO3 has not fallen as much as expected because alkalosis is buffering it. Classic example: DKA patient who has also been vomiting or receiving diuretics.
Normal anion gap metabolic acidosis. Causes: diarrhea (most common — HCO3 loss), renal tubular acidosis, saline infusion, urinary diversion. The acidosis is from HCO3 loss or failure to regenerate HCO3, not from unmeasured anion accumulation.
For every 1 g/dL drop in albumin below 4.0, the AG falls by ~2.5 mEq/L. Critically ill patients with albumin 2.0 g/dL have a baseline AG reduction of 5 mEq/L — always correct the AG in these patients.
Expected pCO2 = 1.5 x HCO3 + 8 (+/-2). If measured pCO2 is higher than expected: concurrent respiratory acidosis. If lower: concurrent respiratory alkalosis. Checks whether respiratory compensation is appropriate.
No. Full interpretation requires pH, pCO2, clinical context, and physician assessment. This provides the mathematical components. All decisions require a licensed healthcare provider.
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