A patient has serum sodium 138 mmol/L, chloride 98 mmol/L and bicarbonate 14 mmol/L. What is the anion gap?

Answer and explanation

Correct answer: B. 26 mmol/L

  1. Step 1: The anion gap is Na - (Cl + HCO3).
  2. Step 2: 138 - (98 + 14) = 26 mmol/L.
Answer
26 mmol/L.
Why not the others: '40 mmol/L' ignores bicarbonate, so it is not the anion gap; '250 mmol/L' adds all three ions instead of subtracting chloride and bicarbonate; '30 mmol/L' adds a potassium-style correction that is not part of the standard formula.

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