What is a normal anion gap?

The normal anion gap is 12 ± 4 mEq/L when calculated as Na⁺ - (Cl⁻ + HCO₃⁻). Some labs use a normal range of 8-12 depending on the analyzer. An anion gap > 16 mEq/L generally indicates an anion gap metabolic acidosis.

What causes a high anion gap metabolic acidosis?

The classic mnemonic MUDPILES lists causes: Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, and Salicylates. An alternative mnemonic is GOLDMARK: Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis.

How do you calculate the anion gap?

The anion gap is calculated as: AG = Na⁺ - (Cl⁻ + HCO₃⁻). Potassium is typically excluded from the calculation. Always correct for albumin in hypoalbuminemic patients: Corrected AG = AG + 2.5 × (4.0 - albumin in g/dL).

What is the delta-delta ratio?

The delta-delta ratio (Δ/Δ) compares the change in anion gap to the change in bicarbonate: (AG - 12) / (24 - HCO₃⁻). A ratio 2 suggests a concurrent metabolic alkalosis.

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Anion Gap Calculator

Calculate anion gap using the standard formula (Na − Cl − HCO₃) with or without potassium. Includes interpretation for metabolic acidosis workup.

Eingaben (mmol/L)

Sodium (Na⁺)

Chloride (Cl⁻)

Bicarbonate (HCO₃⁻)

Potassium (K⁺) (optional) Leave blank to compute AG without K.

Formula

Enter electrolytes to calculate anion gap.

Haftungsausschluss: Nur zu Bildungszwecken. Kein Ersatz für klinisches Urteil.

Interpretation

Reference ranges vary with assay and whether K is included. A commonly used adult range for AG (without K) is ~8-12 mmol/L, but verify locally.

High anion gap suggests unmeasured anions (e.g., lactate, ketoacids, toxins, renal failure).
Normal anion gap (hyperchloremic) metabolic acidosis suggests bicarbonate loss or impaired renal acid excretion.

Clinical pearls

Consider albumin correction for AG in hypoalbuminemia (not included here).
Always interpret with ABG/VBG, lactate, ketones, and clinical context.

References

Kraut JA, Madias NE. Metabolic acidosis: pathophysiology, diagnosis and management. Nat Rev Nephrol. 2010.

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Über dieses Tool

What Is the Anion Gap?

The serum anion gap (AG) is a calculated value representing the difference between measured cations (sodium) and measured anions (chloride + bicarbonate) in the blood: AG = Na⁺ - (Cl⁻ + HCO₃⁻). The "gap" reflects unmeasured anions (albumin, phosphate, sulfate, organic acids) and is a cornerstone of metabolic acidosis evaluation. A normal AG is approximately 12 ± 4 mEq/L (without potassium), though laboratory-specific reference ranges vary with assay methodology.

When to Calculate Anion Gap

Calculate the anion gap whenever metabolic acidosis is identified on ABG/VBG (low pH with low HCO₃⁻) to classify it as anion gap (AGMA) or non-anion gap (NAGMA/hyperchloremic). This distinction is critical because the differential diagnosis and management differ entirely. AG should also be calculated when there is clinical suspicion for toxic ingestion (methanol, ethylene glycol), DKA, lactic acidosis, or uremia.

Anion Gap Calculation Formula and Normal Range

Elevated AG (>12) suggests accumulation of unmeasured anions - use the MUDPILES mnemonic: Methanol, Uremia, DKA, Propylene glycol, INH/Iron, Lactic acidosis, Ethylene glycol, Salicylates. Normal AG metabolic acidosis (hyperchloremic) suggests bicarbonate loss (diarrhea, RTA) or failure to excrete acid. Always correct for albumin: add 2.5 mEq/L for each 1 g/dL albumin below 4.0.

🔑 Klinische Hinweise

Hypoalbuminemia is extremely common in hospitalized patients and masks true AG elevation. A "normal" AG of 10 in a patient with albumin of 2.0 is actually a corrected AG of 15 - elevated.
When AG is elevated, always calculate the delta-delta ratio (ΔAG/ΔHCO₃) to screen for mixed disorders. A ratio <1 suggests concurrent non-AG acidosis; >2 suggests concurrent metabolic alkalosis.
An AG >20 is virtually always pathological and warrants urgent investigation. An AG >30 suggests severe toxin exposure or multi-organ failure.
Some laboratories include potassium in the AG formula: (Na + K) - (Cl + HCO₃), with a higher reference range (~16 ± 4). Know which formula your lab uses.

Schlüsselreferenzen

Emmett M, Narins RG. Clinical use of the anion gap. Medicine (Baltimore). 1977;56(1):38-54.
Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162-174.
Berend K, et al. Physiological approach to assessment of acid-base disturbances. N Engl J Med. 2014;371(15):1434-1445.

Formel zuletzt überprüft: Februar 2026