Final answer:
Giardia trophozoites are detected using a Direct smear fecal test, part of the O&P exam, which is critical in diagnosing giardiasis.
Step-by-step explanation:
Giardia trophozoites can be found on a fecal test known as a Direct smear. This type of stool ova and parasite (O&P) exam involves the direct examination of a stool sample for the presence of cysts and trophozoites, which are key in diagnosing giardiasis, a type of gastroenteritis caused by the protozoan parasite Giardia lamblia. It's important to note that multiple stool samples may be needed over several days for accurate diagnosis.