Three formulas for the anion gap

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Anion gap = measured cations – measured anionsa
Anion gap = unmeasured anions – unmeasured cations
  • a Here, “measured” refers to the cations and anions (sodium, chloride, and bicarbonate) typically included in the anion gap calculation, and “unmeasured” refers to any cations or anions that are not accounted for in the anion gap calculation.