Anion gap in dogs: hyperchloraemic metabolic acidosis
2-year-old French Bulldog with 4 days of profuse watery diarrhoea and no vomiting. Well perfused with mild dehydration.
| Parameter | Result | Reference |
|---|---|---|
| Venous pH | 7.24 | 7.35–7.45 |
| Venous pCO₂ | 30 mmHg | 33–45 |
| HCO₃⁻ | 13 mmol/L | 18–24 |
| Sodium | 144 mmol/L | 140–155 |
| Potassium | 3.4 mmol/L | 3.5–5.8 |
| Chloride | 124 mmol/L | 105–118 |
| Lactate | 1.6 mmol/L | < 2.5 |
Which acid–base disorder is present?
chevron_right Show answer and explanation
A. High anion gap metabolic acidosis due to lactic acidosis
The calculated anion gap is normal and lactate is within range. Lactic acidosis occurs with hypoperfusion, which this dog does not have.
B. Respiratory acidosis
In respiratory acidosis pCO₂ is high. Here it is low, as compensation for a primary metabolic disorder.
C. Hyperchloraemic (normal anion gap) metabolic acidosis due to gastrointestinal bicarbonate loss
Correct. Anion gap = (Na + K) − (Cl + HCO₃) = (144 + 3.4) − (124 + 13) ≈ 10 mmol/L, normal. Bicarbonate lost in the diarrhoea is replaced by chloride, with no accumulation of unmeasured acids. The low pCO₂ is the expected respiratory compensation.
D. Respiratory alkalosis with metabolic compensation
With a pH of 7.24 the net disorder is acidaemia; the primary disorder is the one moving in the same direction as the pH, in this case the fall in bicarbonate.
lightbulb Key takeaway
With metabolic acidosis, calculate the anion gap. Normal (hyperchloraemic): diarrhoea, renal tubular acidosis, excess 0.9% saline. High: lactate, ketoacids, uraemic toxins and ethylene glycol (remember "LUKE"). Hypoalbuminaemia lowers the anion gap and can hide an increase.
Test yourself with 10 random questions
Clinical pathology · 100 questions, a different test every time
Related questions
Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.