Tuberculosis (TB) is a serious infectious disease, and accurate diagnosis is crucial for effective treatment and preventing its spread. Blood tests for TB, also known as interferon-gamma release assays (IGRAs), are a modern and reliable method to determine if you have been infected with TB bacteria. These tests analyze a blood sample to assess your immune system’s response to TB proteins.
In the United States, healthcare providers primarily utilize two FDA-approved TB blood tests:
- QuantiFERON®-TB Gold Plus (QFT-Plus)
- T-SPOT®.TB test (T-Spot)
Who Should Consider a TB Blood Test?
TB blood tests are versatile and can be administered to anyone. However, they are particularly recommended for certain populations:
- Individuals Vaccinated with BCG: The Bacille Calmette-Guérin (BCG) vaccine, used in many countries with high TB prevalence, can cause a false positive result on the traditional TB skin test. TB blood tests are not affected by BCG vaccination, making them a more accurate diagnostic tool for vaccinated individuals.
- Individuals Unlikely to Return for a Follow-Up: The TB skin test requires a return visit to a healthcare provider 48 to 72 hours after administration to have the results read. For individuals who may find it challenging to schedule or attend a second appointment, a TB blood test is a convenient alternative as it requires only one blood draw.
- Pregnant Women: TB blood tests are safe for use during pregnancy. While studies on their effectiveness in diagnosing latent TB infection in pregnant women are still ongoing, they remain a valuable tool for assessing TB infection risk in this population.
It’s important to note that while TB blood tests are excellent for diagnosing TB infection, they are not designed to differentiate between active TB disease and latent TB infection. Further tests are necessary to make this distinction.
Understanding the BCG Vaccine and TB Testing
The BCG vaccine is primarily administered to infants and young children in regions where TB is widespread. It is effective in preventing severe forms of TB, particularly in children. However, it’s not routinely given in the United States due to the lower TB prevalence.
If you have received the BCG vaccine, it’s crucial to inform your healthcare provider, especially if you are undergoing TB testing. As mentioned, the BCG vaccine can lead to a false positive TB skin test result. TB blood tests offer a more specific and reliable diagnostic approach in these cases.
Accessing TB Blood Tests
TB testing is readily available through various healthcare channels. You can get tested at your local health department or your primary care physician’s office. Your healthcare provider will determine the most appropriate TB test for your individual circumstances. It’s also worth noting that both public and private health insurance plans generally cover the costs associated with TB testing.
Finding a Testing Center
To locate a TB testing site near you, reach out to your state or local TB control program. These programs can provide information on testing locations and resources.
State TB Programs
Interpreting TB Blood Test Results
Understanding your TB blood test results is essential for appropriate follow-up and care.
Positive TB Blood Test Result
A positive TB blood test result signifies that you have been infected with TB bacteria. It means TB germs are present in your body. It’s crucial to understand that a positive result does not automatically mean you have active TB disease; it indicates TB infection, which could be either latent TB infection or active TB disease. Further tests are needed to differentiate between the two.
Maintaining a Record of Positive Results
Once you have a documented positive TB blood test or TB skin test result, future TB tests may also yield positive results, even after successful treatment for latent TB infection or active TB disease.
Request a written record of your positive TB blood test result from your healthcare provider. This documentation will be valuable if you are required to undergo TB testing again in the future, preventing unnecessary repeat testing and confusion.
Negative TB Blood Test Result
A negative TB blood test result generally indicates that TB infection is unlikely. However, depending on your individual risk factors and clinical presentation, your healthcare provider may recommend further investigations. This is particularly important if:
- You have recently been exposed to someone with active TB disease.
- You have symptoms suggestive of TB disease, such as persistent cough, fever, night sweats, and unexplained weight loss.
- You have a weakened immune system.
Next Steps After Receiving Your Results
If you receive a positive TB blood test result, it’s imperative to consult with your healthcare provider for further evaluation. Additional tests will be conducted to determine whether you have latent TB infection or active TB disease. These tests may include:
- Chest X-ray: To visualize the lungs and identify any abnormalities suggestive of active TB disease.
- Sputum Smear and Culture: If you are coughing up phlegm, a sample will be analyzed to detect TB bacteria.
Based on the results of these tests, your healthcare provider will provide a definitive diagnosis and recommend the appropriate treatment plan.
Further Reading: Diagnosing Tuberculosis
Resources for More Information
What You Need to Know About Tuberculosis Fact Sheet
This fact sheet offers fundamental information about tuberculosis.
Download Fact Sheet
Questions and Answers About Tuberculosis Booklet
This booklet provides detailed answers to common questions about latent TB infection and TB disease.
Download Booklet
