30th April 2024

A 45-year-old woman presents with complaints of fatigue, pallor, and shortness of breath on exertion for the past two months.

A 45-year-old woman presents with complaints of fatigue, pallor, and shortness of breath on exertion for the past two months. She denies any other medical history.

Investigations:

Haemoglobin 95 g/L (120-160)

White cell count 7.2 × 10^9/L (4-11)

Platelets 210 × 10^9/L (150-450)

MCV 75 fL (80-100)

Serum iron low

TSH normal

Which additional investigation is most likely to help with the diagnosis?