You are a medical SHO and have been asked to see a 53 year old man who has been referred in by his GP with symptomatic anaemia with a Hb of 78g/L. He feels weak, achey and tired but his GP was particularly concerned as last Autumn he was training for the Great North Run and he is now struggling to get out of bed. There are no previous results on the system for the patient. 

How do you go about investigating his anaemia?