Impact of Titer of Toxoplasma Immunoglobulin G on the Diagnosis of Ocular Toxoplasmosis

Purpose: To assess the impact of toxoplasma immunoglobulin G (IgG) titers on the diagnosis of active ocular toxoplasmosis.Methods: We retrospectively analyzed the medical records of patients tested for toxoplasma IgG at our uveitis clinic. Active ocular toxoplasmosis was clinically diagnosed based on wide-angle fundus photography and disease progression. Patients with IgG titers ≥ 30 IU/mL were classified as seropositive-high titer, those with IgG titers of 1.6-30 IU/mL as seropositive-low titer, and the remaining patients as seronegative. We compared the proportion of active ocular toxoplasmosis among these groups. Additionally, we evaluated the sensitivity and specificity of each titer and attempted to determine an ideal reference titer for toxoplasma IgG in diagnosing active ocular toxoplasmosis.Results: Out of 824 patients, 86 (10.4%), 88 (10.7%), and 650 (78.9%) were categorized as seropositive-high titer, seropositive-low titer, and seronegative, respectively. Among these patients, 34 in the seropositive-high titer group and 2 in the seropositive-low titer group were clinically diagnosed with active ocular toxoplasmosis. The false-positive rate was significantly different between the groups, being 60.5% in the seropositive-high titer group and 97.7% in the seropositive-low titer group (p < 0.001). The receiver operating characteristic curve indicated that 37.70 IU/mL could be an ideal reference titer for diagnosing ocular toxoplasmosis.Conclusions: The false-positive rate was notably lower (60.5%) in patients with IgG titers ≥ 30 IU/mL compared to those with titers of 1.6-30 IU/mL (97.7%). Therefore, not only the presence of IgG but also the level of titer appears to be important in diagnosing ocular toxoplasmosis.