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

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.