• Coproantigen;
  • Diarrhea;
  • Fecal antigen;
  • Fluorescent antibody;
  • Protozoa;
  • Zinc sulfate

Background: The performance of Giardia diagnostic tests that detect either cysts or fecal antigens has not been thoroughly examined.

Hypothesis/Objectives: We examined the concordance and agreement among 4 Giardia diagnostic tests (2 cyst and 2 coproantigen detection methods) in a colony of dogs chronically and subclinically infected with Giardia.

Animals: Twenty dogs with chronic, subclinical Giardia infection.

Methods: Giardia diagnostic tests were performed repeatedly on each dog over 120 days. Fecal cyst detection methods (ZnSO4 flotation and fluorescent antibody [FAB] coproscopy) were performed 3 times per week. Coproantigen methods (Giardia SNAP test and quantitative ELISA) were performed weekly. Results were analyzed and compared among methods.

Results: When compared with FAB coproscopy, all of the in-house diagnostic tests had excellent positive predictive values (PPVs, 95–99%) at the study prevalence (89%). At lower prevalence rates, ZnSO4, SNAP, and ELISA tests all had good negative predictive values (NPVs), but poor PPVs. There was poor to good agreement among tests by κ analysis.

Conclusion and Clinical Relevance: Our findings show that most commonly used in-house Giardia diagnostic tests have poor agreement with the gold standard method (FAB coproscopy). The in-house tests have good NPVs, but poor PPVs, at prevalence rates common in most clinical settings.