Learning Objective:
Understand and calculate the anion gap, which helps identify the cause of metabolic acidosis.

Formula:

Explanation:

• = Plasma sodium concentration (mEq/L)
• = Plasma chloride concentration (mEq/L)
• = Plasma bicarbonate concentration (mEq/L)

AG estimates the unmeasured anions in plasma and helps differentiate:

• High AG metabolic acidosis → accumulation of acids (lactic acidosis, ketoacidosis, toxins)
• Normal AG metabolic acidosis → loss of bicarbonate with chloride compensation (diarrhea, renal tubular acidosis)

Normal Range:

• AG ≈ 12 ± 4 mEq/L

Example:

Given:

✅ Answer: Anion Gap = 12 mEq/L (normal)