A high percentage of serum samples that test reactive by enzyme immunoassay for anti-Brucella antibodies are not confirmed by the standard tube agglutination test.

We describe a retrospective analysis of Brucella enzyme immunoassay (EIA) IgM and IgG results compared to those of the standard tube agglutination test (SAT). Among 1,091 samples tested, 104 (9.5%) and 24 (2.2%) sera were positive by IgM and IgG EIA, respectively. Supplemental testing by SAT showed that 82.7% (86/104) of IgM EIA-reactive samples and 54.2% (13/24) of IgG EIA-reactive samples were negative by SAT. Testing all EIA screen-reactive samples by SAT is required when evaluating patients for potential brucellosis. Due to the limitations of serology, culture remains the gold standard for detecting Brucella infection.