Review Question - QID 211101

A 66-year-old man presents to the office complaining of fatigue. He reports that for the past year he has been experiencing a progressive decrease in energy. This week he began having some difficulty breathing while climbing the stairs. He denies chest pain or palpitations. He has no other chronic medical conditions and has had no prior surgeries. The patient is found to be anemic. A fecal occult blood test is positive, and a colonoscopy is obtained. The patient is subsequently diagnosed with colorectal cancer. He undergoes a partial colectomy and is started on 5-fluorouracil as adjuvant chemotherapy. Which of the following should be monitored as the patient continues treatment?