30th April 2024

A 15-year-old boy, previously healthy, presents with severe pain in his legs and lower back.

A 15-year-old boy, previously healthy, presents with severe pain in his legs and lower back. He also reports episodes of dizziness and shortness of breath on exertion. He has a family history of a similar condition in his older sister. Physical examination reveals jaundice and mild splenomegaly.

Investigations:

Haemoglobin: 68 g/L (130–170)

MCV: 70 fL (80–96)

White cell count: 11.0 × 10^9/L (4.0–11.0)

Platelets: 180 × 10^9/L (150–400)

Reticulocyte count: Elevated

Which initial investigation is most likely to help establish a diagnosis?