Test Catalog

Test ID: BRCMG    
Brucella Antibody Screen, IgM and IgG, ELISA, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluating patients with suspected brucellosis

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

If Brucella antibody screen, IgM or IgG is either positive or equivocal, then confirmation by Brucella total antibody agglutination testing will be performed at an additional charge.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Brucellosis, major disease in humans and domesticated animals, is a systemic bacterial infection caused by Gram negative coccobacilli of the genus Brucella. Brucellosis is a zoonotic disease and a variety of domestic animals serve as reservoir species: Brucella infects goats (Brucella melitensis), cattle (Brucella abortus), swine (Brucella suis), and dogs (Brucella canis). Transmission to humans results from direct contact with infected animals, exposure to infectious aerosols, or ingestion of unpasteurized dairy products; human-to-human transmission does not occur. While few cases are reported in the US, the majority of cases occur in the Mediterranean region, Western Asia, and parts of Latin America and Africa. Three species of Brucella commonly cause disease in humans: B melitensis, B suis, and B abortus. Clinical manifestations of brucellosis consist of fever, sweats, malaise, weight loss, headache, and weakness. The onset may be insidious or acute, generally beginning within 2 to 4 weeks after exposure. Any organ or system of the body may be involved, although death is uncommon. Presumptive diagnosis of brucellosis can be made by detection of high or rising titers of specific antibodies, typically to smooth lipopolysaccharide (S-LPS), a major antigenic virulence determinant. Serologic tests using S-LPS can detect antibody to the three major Brucella species due to this shared epitope. IgM antibodies appear during the first week of infection followed by a switch to IgG synthesis during the second week. A variety of serologic tests have been used for diagnosis of Brucella infection. Detection of anti-Brucella antibodies using ELISA has been demonstrated to be a sensitive diagnostic approach. However, all specimens testing positive by an ELISA should be confirmed by an agglutination method as a means to increase assay specificity.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.






Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

In the acute stage of the disease, there is an initial production of IgM antibodies followed closely by production of IgG antibodies. IgG-class antibodies may decline after treatment; however, high levels of circulating IgG-class antibodies may be found without any active disease.


Rising levels of specific antibody in paired sera can be regarded as serological evidence of recent infection. The presence of specific IgM in a single specimen may also indicate a recent infection, although IgM-class antibodies may persist for months following acute disease.


The CDC recommends that specimens testing positive for IgG or IgM by ELISA be confirmed by a Brucella-specific agglutination method.(1)


The CDC/Council of State and Territorial Epidemiologists case definition for human brucellosis states that the laboratory criteria for diagnosis includes 1) isolation of Brucella species from a clinical specimen, 2) four-fold or greater rise in Brucella agglutination titer between acute- and convalescent-phase serum specimens obtained more than 2 weeks apart and studied at the same laboratory, and/or 3) demonstration by immunofluorescence of Brucella species in a clinical specimen.


Positive results by ELISA that are not confirmed by Brucella-specific agglutination may represent false-positive screening results. If clinically indicated, a new specimen should be tested after 14 to 21 days.


If results of ELISA are negative and a recent infection is suspected, a new specimen should be tested after 14 to 21 days.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test utilizes antigen derived from Brucella abortus strain W99. However, significant cross-reactivity exists for other Brucella species (except B canis) and, therefore, the assays should not be used to differentiate infection at the species level.


B canis, a rare cause of brucellosis, may not be detected by this method.


Detection of specific IgM or IgG-class antibody to B melitensis and B suis by this method has not been determined.


ELISA tests are intended to be used as a screen only. Positive results should be followed up using an agglutination assay for confirmation. Results must be used in conjunction with symptoms, patient history, and other clinical findings.


B abortus strain RB51 is used for vaccination of animals in the US. There are currently no serologic tests to detect an antibody response to strain RB51 in humans. Per CDC guidelines, routine clinical serology tests for Brucella do not detect an antibody response to strain RB51. Note that other strains besides RB51 may be used for vaccinating animals outside of the US.(2)

Supportive Data

According the manufacturer's package insert, 127 patient samples testing positive with the Rose-Bengal test were also examined with the Eurroimmun anti-Brucella abortus ELISA, and 160 blood donors were tested. Data from these studies were as follows for anti-B abortus:

-IgG: sensitivity, 78.0%; specificity, 98.0%

-IgM: sensitivity, 56.0%; specificity, 98.0%

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Public health consequences of a false-positive laboratory test result for Brucella-Florida, Georgia, and Michigan, 2005, MMWR Morb Mortal Wkly Rep 2008 Jun 6;57(22);603-605

2. Gunes H, Dogan M: False-positivity in diagnosis of brucellosis associated with Rev-1 vaccine. Libyan J Med 2013;8:20417

3. Corbel MJ: Brucellosis: an overview. Emerg Infect Dis 1997;3:213-221

4. Araj GF, Lulu AR, Saadah MA, et al: Rapid diagnosis of central nervous system brucellosis by ELISA. J Neuroimmunol 1986;12:173-182