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Anion Gap Normal — FRCA Primary MCQ

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ModeratePhysiology - Endocrine & MetabolicAnion Gap NormalFRCA Primary

The normal anion gap is approximately:

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Correct answer: D — 8-12 mmol/L

Anion gap = [Na+] - ([Cl-] + [HCO3-]). Normal value is approximately 8-12 mmol/L (or 12-16 mmol/L if K+ is included). The gap represents unmeasured anions (albumin / phosphate / sulphate / organic acids). An elevated anion gap metabolic acidosis (MUDPILES: methanol / uraemia / DKA / propylene glycol / isoniazid / lactic acidosis / ethylene glycol / salicylates).

Reference: Power Kam 2018 Principles of Physiology for the Anaesthetist