Which of the following best describes how protozoa and helminths are typically detected in stool testing?

• A. Protozoa by eggs/larvae; helminths by cysts/trophozoites
• B. Protozoa by cysts/trophozoites and antigen tests; helminths by eggs/larvae
• C. Protozoa by bacterial cultures; helminths by serology
• D. Protozoa by serology; helminths by blood smear

Answer: (B)

Stool parasite detection centers on the forms that parasites shed in feces. Protozoa are identified by looking for their cysts or trophozoites under the microscope, and many laboratories also use antigen tests to detect protozoan infections (for example, Giardia, Cryptosporidium, and Entamoeba histolytica). Helminths are identified primarily by finding their eggs or larvae in stool samples, which is the standard microscopic approach for detecting worm infections. This combination—protozoa by cysts/trophozoites with optional antigen tests, and helminths by eggs/larvae—best describes typical stool testing. The other options mix up which forms—or which methods—are used for each type of parasite and don’t reflect standard practice.