IgG Avidity Test for Ocular Toxoplasmosis Diagnosis at a Tertiary Center, Northeast of Iran

Background: The diagnostic methods which are used for acute ocular toxoplasmosis are very important; if the treatment is delayed, it sometimes leads to loss of vision. Fewstudies have been performed to evaluate serological tests used in the diagnosis of acute ocular toxoplasmosis. Objective: To evaluate the immunoglobulin (Ig) M, G and IgG avidity tests for diagnosis of acute ocular toxoplasmosis in the northeast of Iran. Methods: A cross-sectional study was carried out from January 2014 to December 2016. After an opthalmic examination was conducted by a retina specialist, 16 typical acute and 34 typical chronic ocular toxoplasmosis cases were included in this study. Information on clinical manifestations, age and occupation was recorded. Anti-Toxoplasma IgG, IgM and IgG avidity tests were administered on serum samples using the ELISA method. Results: Blurring of vision in all patients was the most clinical presentation. The IgG avidity test could diagnose all acute and recent cases. However, three false positive and one false negative result occurred using the IgM test by ELISA. The false negative result in all likelihood occurred because the patient was at the beginning stage of the infection. Conclusion: The result of this study showed that IgM is not a reliable marker of acute disease. Repetition of the serology tests was proposed in cases with clinical manifestations without detectable antibody titer after approximately two weeks. IgG avidity testing results coincided with clinical diagnosis and it could therefore considered to be a reliable method to differentiate between recently acquired and chronic ocular toxoplasmosis.