محاسبه Cut-off point مناسب برای آزمون ELISA جهت تشخیص بروسلوز انسانی در ایران

Background: Finding a reliable diagnostic method for brucellosis is the most challengeable problem. In this study we determined the optimal diagnostic cut-off point for ELISA test.Methods: We gathered 56 confirmed cases of brucellosis. Furthermore blood samples from 126 controls including 73 healthy controls and 53 without brucellosis febrile patients were collected. In all of the cases and controls ELISA Ig G and ELISA Ig M levels were measured and compared with each other by Box plot graph and the Receiver Operating Characteristic (ROC) curve. The sensitivity and specificity of ELISA Ig G and Ig M were fixed in different cut-off values and Ig G and Ig M levels yielding maximal sensitivity plus specificity were selected for determination of optimal cut-off point.Results: The nineteen patients had positive blood cultures for Brucella melitensis. The standard agglutination test results were 1/160 or more in 54 patients. The Box plot graph indicated a high degree of dispersion for Ig G and Ig M data in patients with brucellosis compared with febrile patients without brucellosis and healthy controls. We observed partial overlap for Ig M data (not for Ig G) between cases and controls. The area under ROC curve for discrimination of cases and healthy controls was more for Ig G than Ig M.Conclusions: The ELISA Ig G is more reliable test than ELISA Ig M in diagnosis of brucellosis. Using cut-off of 10 IU/ml and 50 IU/ml have the most sensitivity (92.9%) and specificity (100%) for ELISA Ig G test, respectively.