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

Saleh, Meriam N., Heptinstall, Jack R., Johnson, Eileen M., Ballweber, Lora R., Lindsay, David S., Werre, Stephen, Herbein, Joel F., Zajac, Anne M.
Journal of veterinary internal medicine 2019 v.33 no.3 pp. 1272-1277
Bayesian theory, Giardia lamblia, cats, diagnostic techniques, dog diseases, dogs, feces, fluorescent antibody technique, immunoassays, zinc sulfate, Colorado, Oklahoma, Virginia
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 ZnSO₄ 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 ZnSO₄ centrifugal fecal flotation results.