What is the Anion Gap?
The serum Anion Gap measures the difference between positive ions (Cations like Sodium) and negative ions (Anions like Chloride and Bicarbonate). A "Gap" means there are unmeasured acids hiding in the blood that are disrupting the body's electrical neutrality.
High vs. Normal Gap Acidosis
High Gap (> 12 mEq/L)
Usually means the body is producing excess acid (like Lactic Acid from sepsis or Ketones from diabetes) or the patient has ingested a toxin.
Normal Gap (4 - 12 mEq/L)
Usually means loss of Bicarbonate (e.g., severe Diarrhea) or Renal Tubular Acidosis. This is also called Hyperchloremic Metabolic Acidosis.
Why Correct for Albumin?
The Hidden Acidosis
Albumin is a major unmeasured anion. In sick patients with low albumin (Hypoalbuminemia), the standard gap calculation looks artificially normal because the baseline "gap" is smaller. Correcting for albumin essentially "adds back" the missing negative charge to reveal if an acidosis is truly present.
Frequently Asked Questions
What is the MUDPILES mnemonic?
- Methanol
- Uremia (Kidney Failure)
- DKA (Diabetic Ketoacidosis)
- Propylene Glycol
- Isoniazid / Iron
- Lactic Acidosis
- Ethylene Glycol (Antifreeze)
- Salicylates (Aspirin)
Can Anion Gap be too low?
Tools & Data Verified by the EverydayCalculators Medical Research Team.
Last updated: January 2026.