Evaluation of serological tests for diagnosis of brucellosis

The aim of the present study was to compare serological tests (Rose Bengal [RB]; standard agglutination test [SAT]; enzyme immunoassay [EIA] for detection of IgM, IgA, and IgG; and 2-mercaptoethanol [2-ME] test) that are routinely used in patients prediagnosed with different clinical types of brucellosis (acute, subacute, or chronic), and to evaluate the results of the IgG avidity test. Ninety-two patients having titers≥1/160 as measured by SAT were included in the study. The IgG avidity test was performed in 78 patients who had positive EIA-IgG results. RB test results were positive in 88 (95.7%) patients. A statistically significant correlation was found between a positive EIA-IgM result and the diagnosis of acute brucellosis. When compared to the results of the SAT, the 2-ME test showed a lower titer in 55 (59.8%) patients, and the agreement between the 2-ME test and EIA-IgG was calculated as 84.8%. No statistical difference was found between the 40% avidity index used in the IgG avidity test and avidity maturation time (6 months). From our study, we concluded that (i) the RB and SAT tests are appropriate and reliable tests for the serological diagnosis of brucellosis; (ii) IgM can be used as a marker of acute brucellosis; (iii) the 2-ME test, similar to EIA, can be used to determine IgM levels; and (iv) the IgG avidity test should be standardized.