Calcium

Sodium

Potassium

Metabolic acidosis is commonly classified according to the anion gap. This can be calculated by: (Na+ + K+) - (Cl + HCO3). If a question supplies the chloride level then this is often a clue that the anion gap should be calculated. The normal range = 10-18 mmol/L

Normal anion gap ( = hyperchloraemic metabolic acidosis)

• gastrointestinal bicarbonate loss:
  • prolonged diarrhoea: may also result in hypokalaemia
  • ureterosigmoidostomy
  • fistula
• renal tubular acidosis
• drugs: e.g. acetazolamide
• ammonium chloride injection
• Addison's disease

Raised anion gap

• lactate:
  • shock
  • sepsis
  • hypoxia
• ketones:
  • diabetic ketoacidosis
  • alcohol
• urate: renal failure
• acid poisoning: salicylates, methanol

Metabolic acidosis secondary to high lactate levels may be subdivided into two types: