Which procedure involves a visual examination of the rectum and sigmoid colon with a scope?

• A. Potassium test
• B. PKU test
• C. PSA
• D. Proctosigmoidoscopy

Answer: (D)

The key idea here is identifying a procedure that uses an instrument to directly look at the lining of the distal colon. Proctosigmoidoscopy involves inserting a scope (a proctoscope or a flexible sigmoidoscope) to visually inspect the rectum and sigmoid colon. It is an endoscopic examination, allowing direct visualization of mucosa, and perhaps biopsies or removal of small polyps in that limited portion of the large intestine.

The other items listed are laboratory tests, not endoscopic procedures: a potassium test measures electrolyte levels in the blood, a PKU screen checks for phenylketonuria in newborns, and PSA testing looks for the prostate-specific antigen associated with prostate conditions. They do not involve looking inside the rectum or colon with a scope.