Comparison of diagnostic techniques for detection of Giardia duodenalis in dogs and cats.

Background: An evaluation of currently available in-clinic diagnostic tests for Giardia duodenalis infection of dogs and cats has not been performed. In addition, there is discordance among published diagnostic comparisons. The absence of a true gold standard for detecting Giardia duodenalis also complicates diagnostic evaluations.
Objectives: To evaluate diagnostic tests commercially available in the United States for detecting Giardia duodenalis in dogs and cats, in comparison to a widely used reference test, the direct immunofluorescent assay (IFA), and also to compare the results of 2 methods of analysis: comparison of diagnostic tests to a reference test (IFA) and Bayesian analysis.
Animals: Fecal samples from a convenience sample of 388 cats and dogs located in Colorado, Oklahoma, and Virginia.
Methods: Fecal samples were tested for Giardia duodenalis by zinc sulfate centrifugal fecal flotation and 4 different commercial diagnostic immunoassays. Results were analyzed via Bayesian analysis and by comparison to the IFA as the reference test.
Results: Sensitivity and specificity by comparison to IFA was ≥82% and ≥90%, respectively, for all diagnostic tests in dogs and cats. When analyzed via Bayesian analysis, sensitivity and specificity were ≥83% and ≥95%, respectively. When ZnSO ₄ centrifugal fecal flotation results were combined with immunoassay results, there was no longer a significant difference between the sensitivities of the commercial in-clinic immunoassays.
Conclusion and Clinical Relevance: The Bayesian analysis validates using IFA as the reference test. Differences in commercial in-clinic immunoassay sensitivities can be mitigated when the results are combined with ZnSO ₄ centrifugal fecal flotation results.
(© 2019 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)