A 54‑year‑old woman is reviewed in clinic with several months of fatigue, shortness of breath on exertion, and intermittent paraesthesia in her feet. She also reports some unsteadiness when walking. On examination, she is pale, has a smooth, sore tongue, and shows mild loss of vibration sense in both lower limbs. Hb: 95 g/L (Ref: 115–160) MCV: 118 fL (Ref: 80–100) Reticulocyte count: Low Serum B12: 90 ng/L (Ref: 200–900)