She Didn't Test Positive
We were checking for Giardia, a parasite. The test is run on feces. We are looking for parasite cysts.
We checked the feces from the suspect animal. No cysts to be seen. She did not test positive. Conclusion: She does not have giardiasis.
When testing for an intestinal parasite like Giardia we have to remember that it is normal for shedding to be intermittent. The rule of thumb that work from is to collect fecal samples from a least three different days from the suspect animal.
Usually the reason we are collecting fecal samples from this calf is that her feces are consistently looser than we expect and she is not thrifty in spite of eating well. At the same time we are checking for giardia we can also look for other parasite evidence from both cryptosporidia and coccidia.
It is not uncommon to find evidence of all three parasites in the same fecal samples.