Test Catalog

Interpretive Handbook

Test 89476 :
Brucella Antibody Screen, IgG and IgM, Serum

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

Worldwide, brucellosis remains a major disease in humans and domesticated animals. Brucella infects goats (Brucella melitensis), cattle (Brucella abortus), swine (Brucella suis), and dogs (Brucella canis).(1) The disease has a limited geographic distribution. Few cases occur in the United States, with the bulk occurring in the Mediterranean region, Western Asia, and parts of Latin America and Africa.


Three species of Brucella commonly cause disease in humans: Brucella melitensis, Brucella suis, and Brucella abortus. The acute disease often presents with fever, chills, and malaise; the chronic form also causes abscesses in bone, brain, spleen, liver, and kidney.

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

Evaluating patients with suspected brucellosis

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. Chronic brucellosis shows a predominance of IgG-class antibodies with little or no detectable IgM.


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 Centers for Disease Control and Prevention (CDC) recommends that specimens testing positive for IgG or IgM by enzyme-linked immunosorbent assay (ELISA) be confirmed by a Brucella-specific agglutination method.(2)


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 >2 weeks apart and studied at the same laboratory, 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 7 to 14 days.


If results of ELISA are negative and a recent infection is suspected, a new specimen should be tested after 7 to 14 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 and, therefore, the assays should not be used to differentiate infection at the species level.


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


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


Enzyme-linked immunosorbent assay (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.

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.


Negative (reported as positive, negative, or equivocal)



Negative (reported as positive, negative, or equivocal)

Clinical References Provides recommendations for further in-depth reading of a clinical nature

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

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

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

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