A 49-year-old woman presents with fatigue and exertional dyspnoea. Her haemoglobin is 9.2 g/dL, mean corpuscular volume 72 fL, and ferritin is low. She has no obvious dietary issues. What is the most appropriate next investigation?AStart oral iron and review in 3 months with no further investigationsBArrange colonoscopy and upper GI endoscopyCOrder haemoglobin electrophoresisDTest for intrinsic factor antibodiesERequest a bone marrow biopsyCheck my answer