Which statement is correct for specimen collection and processing?

• A. Stool samples can contain urine.
• B. Stools can be frozen without affecting parasitic structure.
• C. Unpreserved stools can remain at room temperature for up to 72 hours.
• D. Liquid stools are best for detecting ameba and flagellate trophozoites.

Answer: (D)

For detecting motile ameba and flagellate trophozoites, a fresh, liquid stool specimen is essential because trophozoites are fragile and rapidly lose their recognizable features or motility with delay, desiccation, or improper preservation. Examining a fresh liquid sample soon after collection allows direct observation of live trophozoites in a saline or similar mount, which is when their characteristic movement and morphology are best appreciated.

Contaminating urine would introduce artifacts and dilute the specimen, freezing typically destroys trophozoites and can alter parasite structure, and unpreserved stools left at room temperature for extended periods (such as 72 hours) lead to degradation of trophozoites and distortion of findings. Therefore, the statement that liquid stools are best for detecting ameba and flagellate trophozoites correctly reflects how specimen quality and parasite morphology influence detection.