What is Anion Gap?
Anion gap (AG) is the difference between measured cations (Na+) and measured anions (Cl- and HCO3-). It represents unmeasured anions like proteins, phosphates, and organic acids. AG is used to evaluate metabolic acidosis and narrow differential diagnosis.
Anion Gap Interpretation
Normal AG (8-12): Normal, or non-anion gap acidosis (diarrhea, RTA)
High AG (>12): Metabolic acidosis from MUDPILES (Methanol, Uremia, DKA, Propylene glycol, Iron/Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates)
Low AG (<6): Rare, seen in hypoalbuminemia, multiple myeloma, lab error
Albumin Correction
Low albumin reduces measured AG. Each 1 g/dL decrease in albumin decreases AG by ~2.5 mEq/L. Corrected AG accounts for this, revealing hidden acidosis. Formula: Corrected AG = Observed AG + 2.5 × (4 - measured albumin).
Quick Tips
- BMI alone doesn't reflect overall health
- TDEE varies based on activity level
- Consult a healthcare professional for medical decisions
Frequently Asked Questions
When evaluating metabolic acidosis (low HCO3 on basic metabolic panel).
Mnemonic for high AG acidosis: Methanol, Uremia, DKA, Propylene glycol, Iron, Lactic acidosis, Ethylene glycol, Salicylates.
Yes, including metformin (lactic acidosis), salicylates, toxic alcohols.
Albumin is a negative charge. Low albumin falsely lowers AG, masking acidosis.
No, it narrows differential diagnosis. Need additional tests (lactate, ketones, toxicology) for diagnosis.