Anion Gap

Question 1

what is the formula to calculate anion gap?

Answer 1

(sodium + potassium) - (bicarbonate + chloride)

Question 2

what is a normal anion gap?

Answer 2

8-14 mmol/L

Question 3

name some causes of normal anion gap or hyperchloraemic metabolic acidosis

Answer 3

• GI bicarbonate loss (e.g. diarrhoea, ureterosigmoidstomy, fistula)
• renal tubular acidosis
• drugs - e.g. acetazolamide
• ammonium chloride injection
• addison’s disease

Question 4

name some causes of raised anion gap metabolic acidosis

Answer 4

• lactate - e.g. shock, hypoxia
• ketones - e.g. diabetic ketoacidosis, alcohol
• urate - e.g. renal failure
• acid poisoning - e.g. salicylates, methanol
• 5-oxoproline - e.g. chronic paracetamol use