MUDPILES
Anion Gap Metabolic Acidosis
The classic anion-gap culprits — memorize these cold.
What this mnemonic does is take a chemistry panel with an elevated anion gap and turn it into a focused differential. MUDPILES — Methanol, Uremia, Diabetic ketoacidosis (and starvation/alcoholic ketoacidosis), Propylene glycol, Iron or Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates — covers nearly every cause boards will throw at you. Anion gap is calculated as Na minus (Cl + HCO3); over 12 is elevated. AANP exam vignettes pair MUDPILES with a clinical clue: visual loss for methanol, calcium oxalate crystals for ethylene glycol, tinnitus for salicylates. Recognize the triad of vignette finding, anion gap, and toxidrome and the answer falls out.
- MMethanolFormic acid metabolite → anion gap + blindness. Treat with fomepizole + dialysis.
- UUremiaRetained organic acids in renal failure.
- DDKAKetoacid production from insulin deficiency. Look for fruity breath + hyperglycemia.
- PPropylene glycol / ParaldehydeModern culprit is propylene glycol (vehicle in IV lorazepam drips); paraldehyde is historical.
- IIsoniazid / IronINH overdose causes seizures + lactic acidosis; iron toxicity causes hepatic injury.
- LLactic acidosisSepsis, shock, seizures, metformin-associated.
- EEthylene glycolAntifreeze → oxalate crystals in urine + renal failure.
- SSalicylatesClassic mixed acid-base: respiratory alkalosis plus anion-gap metabolic acidosis.
Clinical Context
Use this when you see a high anion gap (>12) on a BMP. Calculate as Na − (Cl + HCO₃). Not every cause is equally likely in every patient — match the mnemonic letters to the clinical stem.
The AANP loves pairing a specific toxidrome with a stem: "empty antifreeze bottle next to patient" → ethylene glycol; "diabetic with fruity breath and Kussmaul respirations" → DKA; "chronic alcoholic found down" → think methanol or starvation ketosis.
Related Mnemonics
- 3 P's — Cardinal Symptoms of Diabetes
Sources
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