Evaluation of Laboratory Techniques for the Diagnosis of Leptospira‐Associated Equine Recurrent Uveitis ( ERU ) With Focus on the Goldmann‐Witmer Coefficient

PURPOSE: To evaluate different laboratory procedures for determining the etiologic diagnosis of equine recurrent uveitis regarding intraocular infection with Leptospira spp. and to establish a diagnostic guideline. MATERIAL AND METHODS: Eighty horses with a history of ERU were ophthalmologically examined. Serum and aqueous humor were collected. Total protein, albumin level, and MAT against Leptospira spp. were evaluated on serum and aqueous humor. PCR for Leptospira spp., EHV-1 and -4 was performed on aqueous humor. Goldmann-Witmer coefficient (GWC) and C-value (CC) were calculated based on MAT. In 42 cases, an additional ELISA was initiated. RESULTS: Forty-six female and 34 male horses of different breeds (mean age 10.9 years; range 3 to 31) were included. By MAT 56/80 horses (70.0%) were identified seropositive for Leptospira spp. MAT results were positive for Leptospira spp. in aqueous humor of 47/80 (58.8%) patients. PCR tested 16/80 (20.0%) positive, ELISA detected 13/42 (31.0%) positive. Neither EHV-1 nor EHV-4 were detected by PCR. Calculating GWC gives evidence suggestive of intraocular involvement with Leptospira spp. in 53/80 (66.3%) at the level ≥ 3. Setting GWC ≥ 3 as gold standard, ELISA and C ≥ 2 closely matched this threshold, showing high accuracy (95.2%; 91.3%), sensitivity (86.7%; 84.9%), and strong agreement (V = 0.90; V = 0.81). PCR was less accurate (53.8%) and sensitive (30.2%) compared to GWC. CONCLUSION: Within this setting, GWC achieved the highest number of positive results for detecting intraocular involvement of Leptospira spp. when compared to PCR, ELISA, and C-value.