Laboratory / Acid-Base

Anion Gap Clinical Calculator

Calculate the serum anion gap, adjust it for albumin, and generate a cautious clinical interpretation with possible causes and suggested next steps.

Clinical safety: This tool supports education and clinical reasoning. It cannot determine the diagnosis or replace history, examination, repeat testing, blood gas analysis, or clinician judgment.

Enter laboratory values

Use values drawn at approximately the same time. The laboratory's own reference interval should take priority.

Sodium (Na⁺) (mEq/L)

Chloride (Cl⁻) (mEq/L)

Bicarbonate / CO₂ (mEq/L)

Albumin (g/dL, optional)

Lab lower reference (mEq/L)

Lab upper reference (mEq/L)

Glucose (mg/dL, optional context)

Patient has concerning symptoms such as confusion, severe weakness, vomiting, deep or rapid breathing, chest pain, fainting, or marked dehydration.

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Results will appear here

Enter sodium, chloride, and bicarbonate, then select Calculate.

How the calculator works

Anion gap = Sodium − (Chloride + Bicarbonate) Corrected AG = measured AG + 2.5 × (4.0 − albumin)

Potassium is not included. Albumin correction is most clinically useful when albumin is below 4.0 g/dL, because hypoalbuminemia can mask a genuinely raised gap.

Common high-gap causes

Lactic acidosis (sepsis, shock, ischemia, severe hypoxemia, some medications)
Ketoacidosis — diabetic, alcoholic, or starvation
Reduced acid excretion in advanced kidney failure or uremia
Selected toxic ingestions (methanol, ethylene glycol, salicylates, propylene glycol)
Medication-related causes such as metformin-associated lactic acidosis

Normal-gap acidosis

Gastrointestinal bicarbonate loss (diarrhea, high-output ostomy, pancreatic/biliary drainage)
Renal tubular acidosis (types 1, 2, or 4)
Large-volume saline infusion producing hyperchloremia
Urinary diversions (ureteroenteric conduits)
Medications such as acetazolamide, topiramate, or spironolactone

Low anion gap

Measurement or specimen error — the most common explanation; repeat the panel
Hypoalbuminemia (each 1 g/dL drop lowers the gap by roughly 2.5 mEq/L)
Increased cationic proteins such as monoclonal gammopathy (e.g. myeloma)
Lithium toxicity, bromide, or iodide accumulation
Severe hypercalcemia or hypermagnesemia, or assay interference

References

Merck Manual Professional: Anion Gap clinical calculator. Cleveland Clinic: Anion Gap Blood Test and Metabolic Acidosis. Cleveland Clinic Journal of Medicine: Evaluating a low anion gap — a practical approach. Normal ranges vary by laboratory and analyzer.