Veterinary Anion Gap Calculator (Dog & Cat)
Calculate the anion gap from sodium, potassium, chloride, and bicarbonate, with species reference ranges and a differential list for high and low results in dogs and cats.
Species
Sodium, Na (mEq/L)
Potassium, K (mEq/L)
Chloride, Cl (mEq/L)
Bicarbonate / Total CO2 (mEq/L)
Formula
AG = (Na + K) − (Cl + HCO3) · most veterinary formulas include potassium.
How to use this tool
The formula
With potassium (most common in veterinary medicine): AG = (Na + K) − (Cl + HCO3). Without potassium: AG = Na − (Cl + HCO3). Always match the formula to the reference range you're comparing against - the two conventions aren't interchangeable.
Reference ranges
Typical textbook ranges with potassium included are roughly 12-24 mEq/L in dogs and 13-27 mEq/L in cats. These shift lower by roughly 8 mEq/L when potassium is excluded. Always confirm against your own lab's reference interval since methodology varies between analyzers.
High anion gap
An elevated gap points to unmeasured anions accumulating in the blood. The classic "big three" to rule out are diabetic ketoacidosis, uremia/renal failure, and ethylene glycol toxicity - also consider lactic acidosis and salicylate toxicity.
Low anion gap
A low gap is less common and most often caused by hypoalbuminemia, since albumin is itself a major unmeasured anion. Also consider bromide toxicity (which spuriously raises measured chloride), lithium toxicity, and paraproteinemia from multiple myeloma.
Frequently asked questions
How do you calculate the anion gap in dogs and cats?
With potassium (most common in veterinary medicine): AG = (Na + K) − (Cl + HCO3). Without potassium: AG = Na − (Cl + HCO3). Example: Na 145, K 4.5, Cl 110, HCO3 18 gives AG = (145 + 4.5) − (110 + 18) = 21.5 mEq/L, which is within the normal dog range.
What causes a high anion gap in a dog or cat?
A high gap reflects unmeasured anions accumulating in the blood. The classic "big three" to rule out are diabetic ketoacidosis (ketone anions), uremia/renal failure (retained anions like phosphate and sulfate), and ethylene glycol toxicity (glycolate/oxalate anions). Also consider lactic acidosis and salicylate toxicity.
What causes a low anion gap?
Hypoalbuminemia is the most common cause, since albumin is itself a major unmeasured anion - low albumin lowers the calculated gap. Also consider bromide toxicity (which interferes with the chloride assay and spuriously raises measured chloride), lithium toxicity, and multiple myeloma/paraproteinemia (cationic paraproteins).
Should I include potassium in the anion gap formula?
Both conventions are used in veterinary medicine. Including potassium is more common and shifts the reference range higher (roughly 12-24 mEq/L in dogs, 13-27 mEq/L in cats) compared to excluding it. Always match the formula you use to the reference range you are comparing against.