Anaemia in a 17 year old student

A 17 year old non-vegetarian Asian female student presented with a three year history of increasing lethargy and shortness of breath during exercise. On examination she was clinically anaemic but had no other physical signs.

Haematological investigations, including a blood film (fig 1⇓), were performed. Her haemoglobin was 85 g/l (normal range 120-160 g/l), mean cell volume was 79 fl (80-96 fl), mean cell haemoglobin was 25 pg (27.3-32.6 pg), haematocrit was 29% (0.36%-0.44%), white blood cell count was 5.0×10⁹/l (4-11×10⁹/l), differential cell count was normal, and platelets were 550×10⁹/l (150-400×10⁹/l).