Your vet will need a very fresh fecal sample. (puppys-place.com)
These are protozoal parasites that we need a fresh fresh fecal sample to do smear on, and if we are lucky, we will see them moving under the microscope. (allfelinehospital.com)
Very fresh fecal samples are needed to detect tapeworms, and it may take multiple samples being evaluated over the course of a few days to find the tapeworm proglottids (egg cases) or ova (which may be free - floating if the proglottid has ruptured). (smallanimalchanel.com)