From the Guidelines
The QuantiFERON-TB Gold test is the preferred method for tuberculosis screening in individuals who have received the BCG vaccine, as it is more specific and not influenced by prior BCG vaccination. The BCG vaccine can cause false positive results on the TB skin test (TST), making it less reliable for individuals who have been vaccinated 1. The TB skin test works by injecting tuberculin purified protein derivative under the skin and measuring the resulting skin reaction 48-72 hours later, but it cannot distinguish between reactions caused by BCG vaccination and actual TB infection.
The QuantiFERON test, on the other hand, is a blood test that measures immune response to TB-specific antigens not present in the BCG vaccine, making it more accurate for people previously vaccinated with BCG 1. According to the 2014 guidelines for the management of persons infected with HIV, the QuantiFERON-TB Gold test is one of the approved methods for detecting latent M. tuberculosis infection, and it performs similarly to TST at identifying HIV-infected individuals with latent tuberculosis infection 1.
Some key points to consider when interpreting test results include:
- Vaccination history: Inform your healthcare provider if you've had the BCG vaccine, as this can affect the interpretation of TB skin test results.
- TB risk factors: Consider your risk factors for TB, such as travel history or exposure to individuals with TB.
- Symptoms: Report any symptoms that may be related to TB, such as cough or fever.
- Test results: The QuantiFERON-TB Gold test is more specific than the TB skin test, but it's still important to consider the results in the context of your overall health and risk factors.
Overall, the QuantiFERON-TB Gold test is a more reliable method for tuberculosis screening in individuals who have received the BCG vaccine, and it should be considered the preferred method for testing in these individuals 1.
From the Research
BCG Vaccine and TB Skin Test/Quantiferon
- The BCG vaccine can affect the results of the tuberculin skin test (TST), leading to false positives 2, 3, 4, 5, 6
- The QuantiFERON-TB Gold test (QFT-G) is more specific for latent tuberculosis infection (LTBI) than the TST, especially in BCG-vaccinated individuals 2, 3, 4, 5, 6
- Studies have shown that QFT-G can be used as an alternative to TST for detecting LTBI, especially in high-risk groups and populations with routine BCG vaccination programs 2, 3
Comparison of QFT-G and TST
- A study found that QFT-G had a higher specificity and negative predictive value than TST for diagnosing LTBI in BCG-vaccinated healthcare workers 2
- Another study found that the addition of QFT-G to TST reduced the number of diagnoses of TB infection and preventive therapy prescribed among BCG-vaccinated contacts 3
- A study comparing QFT-G and TST in patients with systemic lupus erythematosus found that QFT-G was more accurate for detecting LTBI in this population 5
Predictors of Positive QFT-G Results
- Factors associated with a positive QFT-G result include: