From the Guidelines
A positive Brucella IgG with negative IgM result typically indicates past exposure to Brucella bacteria rather than an active infection. IgG antibodies develop later in the infection process and can persist for years after recovery, while IgM antibodies appear early in infection but decline more quickly 1. This pattern suggests you had brucellosis in the past but have likely recovered. However, interpretation should always consider clinical symptoms. If you're currently experiencing symptoms like fever, fatigue, joint pain, or night sweats, consult your healthcare provider as chronic brucellosis can sometimes persist with positive IgG only.
Some key points to consider in the interpretation of Brucella serology include:
- The sensitivity of blood cultures varies from 15 to 70% depending on laboratory practices 1
- Newer generation serological tests may help in interpreting results on individuals from endemic areas or those with chronic disease 1
- In endemic countries, Brucella is a very common cause of native vertebral osteomyelitis (NVO) and a false-negative serologic test is unusual in patients with brucellar NVO 1
- A false-positive test for Brucella serology is more likely in non-endemic areas, and an image-guided aspiration biopsy may be warranted in such cases 1
Additional testing such as blood cultures, PCR, or repeat serological tests might be needed for a definitive diagnosis. If you have no symptoms, no treatment is typically required for past exposure. Your doctor may recommend follow-up testing to monitor antibody levels, especially if you have ongoing risk factors like occupational exposure to animals or consumption of unpasteurized dairy products. It is essential to consult with a healthcare provider for proper interpretation of test results and guidance on further management.
From the Research
Brucella IgG Positive IgM Negative Interpretation
- The presence of IgG antibodies against Brucella indicates a past or current infection 2, 3.
- A negative IgM result in the presence of positive IgG suggests that the infection is not acute, as IgM antibodies are typically indicative of acute infection 2, 3.
- However, the interpretation of Brucella serology results can be challenging, and a single positive IgG or IgM result should be considered in the context of the patient's clinical history and epidemiological context 2, 3.
- Studies have shown that patients with only positive IgG antibodies can be diagnosed with brucellosis, while those with only positive IgM antibodies are less likely to be diagnosed with the disease 2, 3.
- Double-positive (IgG- and IgM-positive) serology patterns are more likely to be associated with a diagnosis of brucellosis 3.
Clinical Implications
- The treatment of brucellosis typically involves a combination of antibiotics, such as doxycycline and streptomycin or doxycycline and rifampin 4, 5, 6.
- The choice of treatment regimen may depend on the severity of the disease, the patient's age and health status, and the presence of any underlying medical conditions 4, 5, 6.
- In patients with a positive IgG result and a negative IgM result, the treatment approach may depend on the clinical presentation and the presence of any symptoms or signs of active infection 2, 3.
Laboratory Diagnosis
- The diagnosis of brucellosis typically involves a combination of laboratory tests, including serology, blood culture, and PCR 2, 3.
- The interpretation of Brucella serology results should be done in the context of the patient's clinical history and epidemiological context, and should be confirmed by other laboratory assays when possible 2, 3.