Tear secretory IgA: evaluation of usefulness as a diagnostic marker in herpetic keratitis

In a South Indian study, an 'in-house' enzyme-linked immunosorbent assay (ELISA) was developed to evaluate the potential of herpes simplex virus (HSV)-specific tear secretory IgA (sIgA) in the diagnosis of herpes simplex keratitis (HSK). The presence of HSV-specific tear sIgA was found to be diagnostic in 20.28% of cases. The usefulness of the sIgA ELISA system was evaluated against HSV isolation, which is the 'gold standard' and HSV antigen detection, a more sensitive, commonly employed method. Analysis of HSV-specific IgG and IgM results showed their failure as reliable indicators of active or ongoing infection. Comparison of sIgA ELISA with culture as 'gold standard' showed its sensitivity, specificity, and positive and negative predictive values to be 60% (95% CI 36.4-80), 93.2% (95% CI 86.7-96.8), 60% (95% CI 36.4-80), and 93.2% (95% CI 86.7-96. 8), respectively. This study is the first report on the complete evaluation of the usefulness of tear anti-HSV sIgA in the laboratory diagnosis of HSK, taking into account both epithelial and stromal keratitis cases.