Alicewave, it's not exactly true that crypto is only detectable with expensive testing. Crypto is one of the coccidians and you CAN see oocysts in a fecal float and diagnose it that way. However, any of the microscopic parasites are tough to get accurate samples in a float. Affected animals don't always shed the oocysts in their feces, sometimes the colony is high up in the small intestines and the oocysts don't make it downstream. Other times the fecal float isn't mixed well enough (you really need to beat the crap out of that crap!) and the oocysts stay on the bottom of the vial instead of floating up to the top of the prep solution where they can make it to the microscope slide.
A fecal float that is positive for crypto from a microscope slide is considered definitive and no expensive testing needs to be done, but a "none seen" result is not considered diagnostic. So vets do a gastric or epigastric lavage to flush out the entire digestive tract if they have a strong enough suspicion that the animal has been colonized by crypto, and analyze the effluent for parasites. That is an invasive procedure and therefore rather expensive.
Also, lots of vets went to school back before they first started quantifying the various coccidial strains in the mid-1990s. If they see oocysts on a slide they diagnose coccidia, which is accurate, as crypto is one of the coccidians, they just don't have the tools to take it to the next level and diagnose which coccidian is in the slide. So a lot of the coccidia that is diagnosed may be crypto. If treatment with Albon or other sulfa drugs is ineffective, they often send the original slides to a lab for molecular testing to get a fully accurate quantification as to which coccidia you are dealing with, and that can cost around $600-900 USD.
The Zombie Mama is here!