My Mom Is 85 And Has A Blood Count Of

My mom is 85 and has a blood count of 7.1. They are transfusing her today because they have not located where he r slow bleed is. She has copd and congestive heart failure. They want to give her a colonoscopy to see if the slow bleed is in gi track. Would it be better to give her a full body scan like a pet scan so they can get to the heart of the problem fast ? thanks Cynthia z.