What anion gap value defines primary anion gap metabolic acidosis?

What anion gap value defines primary anion gap metabolic acidosis?

• A. >15
• B. >20
• C. >25
• D. >30

Answer: (B)

The key idea is that the anion gap reflects unmeasured anions in the blood. It’s calculated as Na minus (Cl plus HCO3), and the normal range is about 8–12 mEq/L (some labs use up to ~14). When unmeasured acids accumulate—lactate, ketoacids, toxins, sulfate, phosphate—the gap rises, signaling a high anion gap metabolic acidosis. A value greater than 20 mEq/L is the conventional cut-off used to define a primary high anion gap metabolic acidosis, indicating the acidosis is driven by excess unmeasured anions rather than a pure bicarbonate loss with chloride compensation. Values just above the upper limit can occur with mild elevations or mixed disorders, but crossing 20 is the standard threshold for this definition.

The key idea is that the anion gap reflects unmeasured anions in the blood. It’s calculated as Na minus (Cl plus HCO3), and the normal range is about 8–12 mEq/L (some labs use up to ~14). When unmeasured acids accumulate—lactate, ketoacids, toxins, sulfate, phosphate—the gap rises, signaling a high anion gap metabolic acidosis. A value greater than 20 mEq/L is the conventional cut-off used to define a primary high anion gap metabolic acidosis, indicating the acidosis is driven by excess unmeasured anions rather than a pure bicarbonate loss with chloride compensation. Values just above the upper limit can occur with mild elevations or mixed disorders, but crossing 20 is the standard threshold for this definition.