Formula:

Anion Gap = Sodium – (Chloride + Bicarbonate)

typically considered normal if ≤ 12

Formula:

Urinary Anion Gap = Urine Sodium + Urine Potassium – Urine Chloride

Interpretation:

• Negative UAG (-30 to -50 mmol/L or more negative): Suggests gastrointestinal loss of bicarbonate or renal tubular acidosis type 2.
• Positive UAG (>0 to +30 mmol/L): Suggests distal renal tubular acidosis type 1 or inadequate renal acidification.

Normal Anion Gap Metabolic Acidosis:
Gastrointestinal losses:
Diarrhea
Fistulas (e.g., pancreatic, biliary)
Ileal resection
Renal losses:

Toluene solvent inhalation
Proximal renal tubular acidosis (RTA type 2)
Distal renal tubular acidosis (RTA type 1) – partial cases present with normal gap
Certain medications (e.g., acetazolamide, amphibolic meds)
Exogenous acids:
Total parenteral nutrition (TPN) with excessive chloride
Other:
Severe hypoadrenocorticism (Addison’s disease)
Carbonic anhydrase inhibitors
Ureteral diversion (eg, ileal loop)
Iatrogenic