An elderly patient presents with a prolonged history of weakness and lethargy. On examination he is found to be anemic and stool is positive for occult blood. Which of the following is the investigation of choice:

Answer is A (Colonoscopy) Colonoscopy is the investigation of choice in elderly patients presenting with occult fecal blood and anemia to evaluate the possibility of a colorectal cancer. 'Colonoscopy is the test of choice in a case with occult fecal blood, rectal bleeding, anemia, or weight loss in an older patient, all of which suggest the possibility of colorectal cancer' - 'Primary Care Medicine' (Lippincott)6th/522 'In elderly patients who often tolerate barium enema badly, colonoscopv should be the first-line investigation for unexplained rectal bleeding or anemia and is the investigation of choice for all patients with a positive fecal occult blood test' - General surgical operations by Kirk (Elsevier) 2006/228.