What is the correct formula for calculating the anion gap?

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Multiple Choice

What is the correct formula for calculating the anion gap?

Explanation:
The idea is to estimate unmeasured anions by comparing the major measured cations to the major measured anions. You add the principal cations (sodium, and often potassium) and subtract the principal anions (chloride and bicarbonate). That gives the anion gap: Na+ + K+ − (Cl− + HCO3−). Including potassium increases the normal range a bit (roughly 12–16 mEq/L if potassium is included, vs about 8–12 without it). For example, if Na is 140, K is 4, Cl is 100, and HCO3− is 24, the gap is 140 + 4 − (100 + 24) = 20, indicating an elevated gap due to unmeasured anions.

The idea is to estimate unmeasured anions by comparing the major measured cations to the major measured anions. You add the principal cations (sodium, and often potassium) and subtract the principal anions (chloride and bicarbonate). That gives the anion gap: Na+ + K+ − (Cl− + HCO3−). Including potassium increases the normal range a bit (roughly 12–16 mEq/L if potassium is included, vs about 8–12 without it). For example, if Na is 140, K is 4, Cl is 100, and HCO3− is 24, the gap is 140 + 4 − (100 + 24) = 20, indicating an elevated gap due to unmeasured anions.

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