Non-Anion Gap Metabolic Acidosis, Causes and Differential Diagnosis (USED CARP and HARD UP)

ACID-BASE DISTURBANCES, DDx

Causes of Normal Anion Gap (Hyperchloremic) Metabolic Acidosis

Non-anion gap metabolic acidosis is by definition hyperchloremic. Bicarb is lost from the system directly without taking up the hydrogen from a conjugate acid and leaving behind a conjugate base to increase the AG.
Causes of normal anion gap metabolic acidosis can be broken into two:
1) G.I causes (GI bicarb loss) e.g. Diarrhea / Laxatives; Fistula (pancreatic, biliary), Uretero-intestinal diversion  (ileal conduit)
2) Renal Causes e.g. RTA, Carbonic anhydrase inhibitors, renal failure.

USED CARP

Ureterosigmoid loop
Small bowel fistula
Extra chloride
Diarrhea
Carbonic anhydrase inhibitors -Acetazolamide
Adrenal
RTA (Renal tubular acidosis) – (Type 1 Distal or Type 2 Proximal)
Pancreatic fistula

FUSED CARS

  • Fistula (pancreatic, biliary)
  • Uretero-gastric conduit
  • Saline admin (dilutional acidosis)
  • Endocrine (hyper-PTH)
  • Diarrhea
  • Carbonic anhydrase inhibitor (acetazolamide)
  • Ammonium chloride
  • Renal tubular acidosis
  • Spironolactone

HARDUP

Hyperalimentation,
Acetazolamide and other carbonic anhydrase inhibitors,
Renal tubular acidosis,
Diarrhea,
Ureteroenteric fistula,
Pancreaticoduodenal fistula

 

Resources

Kraut JA, Madias NE. Differential diagnosis of nongap metabolic acidosis: value of a systematic approach. Clin J Am Soc Nephrol. 2012;7(4):671–679. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3315347/

print