Diagnosis of feline giardiasis in feces can be made by a variety of methods. Centrifugation with the use of zinc sulfate and routine microscopy has been considered the best way to detect Giardia spp. Other methods use antibodies to detect the presence of Giardia antigen (ELISA method) or Giardia oocysts (IFA method).

A comparison study of the above methods was undertaken with 8 young adult cats inoculated with a human Giardia isolate. Feces were collected from these cats on weeks zero, 3, 6, 9, 12 and 15. The IFA method was negative at week zero and positive on all samples thereafter. Relative to the IFA results, the zinc sulfate test was found to have 87.5% sensitivity and 75% specificity, whereas the antigen ELISA had 95% sensitivity and 100% specificity. The IFA and Giardia antigen ELISA gave comparable results. The centrifugation method was far superior to routine fecal flotation for detection of Giardia. However, when small numbers of cysts were present, the IFA and Giardia ELISA methods were more sensitive than the zinc sulfate assay.

Fenbendazole treatment of cats (and dogs) infected with Giardia has been efficacious and safe, and is considered superior to metronidazole. Albendazole is also efficacious, but there are reports of toxicity with this drug. A Giardia vaccine is available but its usefulness in treating infected cats is unclear. This vaccine has been shown to reduce clinical signs in dogs with giardiasis, and lessen or eliminate cyst shedding when used as a preventative.