4th May 2024

A 45-year-old woman presents to the clinic complaining of fatigue, shortness of breath on exertion, and tingling sensation in her hands and feet.

A 45-year-old woman presents to the clinic complaining of fatigue, shortness of breath on exertion, and tingling sensation in her hands and feet. She follows a strict vegan diet and does not take any supplements. Her vital signs are within normal limits. Physical examination reveals pallor and decreased vibration sense in her lower extremities.

Investigations:

Haemoglobin 95 g/L (115–150)

Mean corpuscular volume (MCV) 110 fL (80–100)

Serum vitamin B12 100 pmol/L (148–771)

Which is the next management step?