Anion gap = (Na + K) - (Cl + HCO3)
A 'normal' anion gap is 10 to 18mmol/l (which can be recalled as roughly the ages you attend secondary school for)
Causes of a raised anion gap may be recalled as LUKES:
- lactic acid (shock, infection, hypoxia)
- urate (renal failure)
- ketones (diabetes, alcohol)
- ethylene glycol/methanol
- salicylate
A more comprehensive list can be recalled by 'cute dimples' = cyanide, urate, toulene, ethylene glycol, diabetic ketoacidosis, isoniazid, methanol, propylene glycol, lactic acid, salicylates
Causes of a metabolic acidosis with a normal anion gap can be recalled as FUSEDCARS:
- fistula (pancreatic)
- uretogastric conduits
- saline administration
- endocrine (hyperparathyroidism)
- diarrhoea
- carbonic anhydrase inhibitors (acetazolamide)
- ammonium chloride
- renal tubular acidosis
- spironolactone
Hopefully thats demystified the anion gap for you.
