Clinical performance of the IMMY cryptococcal antigen lateral flow assay in dogs and cats

Abstract

Background: Cryptococcal lateral flow antigen assays (CLFAs) have been assessed in comparison to the latex cryptococcal antigen agglutination test but their clinical performance is unknown. Objective: Determine clinical performance of IMMY CLFA (Immuno-Mycologics Inc, Oklahoma) using patients with and without cryptococcosis as the reference standard. Animals: One-hundred ninety-seven serum samples from client-owned dogs and cats. Methods: Review of medical records of a referral population of dogs and cats that had CLFA performed between 2012 and 2020. Animals were classified as cryptococcosis positive (Cr+) or negative (Cr−) based on clinical information. Clinical diagnosis was used to calculate positive and negative percent agreement of the CLFA. Results: Twelve specimens (4 canine, 8 feline) were obtained from Cr+ animals and had positive CLFA results. One-hundred eighty-five specimens (139 canine, 46 feline) were collected from Cr− animals. Negative CLFA results were recorded in 129 canine and 44 feline Cr− samples. Positive CLFA results were noted for 10 canine and 2 feline Cr− samples. Positive percent agreement of CLFA was 100% (confidence interval [CI], 39.8%-100% dogs; 63.1%-100% cats). Negative percent agreements were 92.8% (CI, 87.2%-96.5%) for dogs and 95.7% (CI, 85.2%-99.5%) for cats. Conclusions and Clinical Importance: A negative IMMY CLFA result enables reliable exclusion of cryptococcal infection in dogs and cats. By contrast, a positive result must be interpreted cautiously and further testing should be performed to verify a diagnosis of cryptococcosis.