Question category: Haematology
A 68 year old female with CLL presents with tiredness and shortness of breath on exertion which has been worsening over the last month. Her bloods reveal a haemoglobin of 7.0 g/dL, low normal platelets, elevated white cell count and an elevated bilirubin although her other LFTs are normal. Which investigation will provide the likely cause of the anaemia?