Assessment of index value performance of enzyme immunoassay test in predicting the diagnosis of human brucellosis

Clinical presentation of brucellosis is variable. Therefore, it must be confirmed with laboratory findings. Standard tube agglutination test (STAT) is commonly used for diagnosis of brucellosis. ELISA tests differentiate between IgM and IgG antibodies. However, there are evidences revealing that they do not have sufficient specificity. This study aimed to determine an ELISA optimal index value in the diagnosis of brucellosis. Brucella STAT and ELISA IgM/IgG tests of patients admitted to the hospital with signs and symptoms of brucellosis between January 2017 and December 2019 were evaluated in the Microbiology Laboratory. ELISA IgM and IgG serum median index value was significantly higher in STAT positive (1 ≥ 1:160) group (p < 0.001 for both). By ROC analysis of 117 patients, when the IgM index value was determined to be 2.44, the sensitivity, specificity, positive and negative predictive values were 85.7%, 71.4%, 60%, and 90.9%, respectively, and when the IgG index 7.85 was determined, these values were 85.7%, 53.7%, 36.7%, and 92.3%, respectively was detected. In this study, it was revealed that Vircell Brucella had a good clinical diagnostic performance for index value of 2.44 for IgM test kit and 7.95 for IgG test kit. If the diagnosis of brucellosis is correctly predicted with index values in Brucella IgM and IgG tests before STAT analysis, they can be used in the process of clinical decision. In addition to the results of Brucella ELISA, reporting index values and determining optimal index values for each laboratory can help the diagnosis of brucellosis.