Dealing with a possible tuberculosis (TB) diagnosis can feel overwhelming, but understanding the tests involved can bring clarity and peace of mind. A “qft test,” also known as the QuantiFERON-TB Gold Plus (QFT-Plus) test, offers a modern and efficient approach to detecting TB infection. In this article, you’ll learn how the test works, when it’s used, and what its results could mean for you. It’s crucial to understand that this information is for general knowledge purposes only, and nothing substitutes for consulting with your healthcare provider about any health concerns.
Decoding the QFT Test: How It Works
Unlike the traditional tuberculin skin test (TST), which requires two visits to your doctor’s office, the qft test needs just one blood sample. This makes the qft test useful for people who have trouble making multiple appointments, as a leading healthcare company Labcorp explains. Labcorp emphasizes the ease and flexibility of a qft test.
What Happens During a QFT Test?
When you go for a qft test, a healthcare professional will draw a small amount of your blood. Your blood then gets mixed with specific TB antigens. Think of these antigens as “red flags” for your immune system.
If you’ve previously been infected with TB, your immune cells will “remember” those TB germs and start releasing a chemical messenger called interferon-gamma (IFN-gamma). This reaction is what the lab technicians are looking for. Your blood is then analyzed for the presence of IFN-gamma, providing a quantifiable immune response to aid in the diagnosis of TB. They put your blood sample through a lab test called an enzyme-linked immunosorbent assay, or ELISA for short.
If the ELISA test shows high levels of IFN-gamma, it means your immune system has been exposed to TB.
When is the QFT Test Recommended?
While TB is far less prevalent today than in the past, it’s still an important health concern. This is especially true for individuals with weakened immune systems and those who’ve been in contact with someone who has active TB. So when might a healthcare provider suggest a qft test? The Centers for Disease Control and Prevention (CDC) lists these potential reasons:
- Possible TB exposure
- People entering healthcare or other high-risk workplaces
- Individuals moving to the United States from a country with high TB prevalence
- People living in crowded environments where TB spreads easily, like shelters
In contact investigations, if an initial test is negative, a confirmation test might be advised 8-10 weeks following exposure. This is indicated by the qft test documentation QuantiFERON-TB Gold Plus FAQ for Healthcare Professionals.
Understanding Your Results: Positive, Negative, or Indeterminate
So you’ve had your blood drawn for the qft test; what happens next? It takes a few days for the lab to process your blood sample and send the results to your healthcare provider. Here’s a rundown of what each potential outcome might mean.
Positive QFT Test Results:
A positive qft test means your blood sample contained a high level of IFN-gamma. A positive qft test shows you’ve been infected with the bacteria that cause tuberculosis, Mycobacterium tuberculosis. Now, this doesn’t necessarily mean you have active TB, which is the form that makes you sick and contagious. The qft test doesn’t differentiate between active TB disease and latent TB infection, where the bacteria are present but dormant.
However, according to QuantiFERON.com, a positive qft test is highly specific and strongly suggests a true TB infection.
Negative QFT Test Results:
If your qft test result comes back negative, you most likely don’t have a TB infection. Keep in mind; however, that no test is foolproof.
Indeterminate QFT Test Results:
Sometimes, a qft test produces indeterminate results. This result can occur if your immune system wasn’t able to mount a measurable response to the TB antigens. Your doctor may advise a repeat qft test or use other tests, like a TB blood test, to get a more conclusive diagnosis. This may involve exploring additional lab testing options or considering a tb blood test for further insights.
QFT Plus vs. Tuberculin Skin Test (TST): How do They Stack Up?
In the past, the tuberculin skin test, or TST, was the standard way to check for TB infection. With the advancement of medical diagnostics, newer tests like the QFT Plus offer a better option. They have several notable differences, as outlined in a comprehensive review by the healthcare firm, Quest Diagnostics.
We’ve created a table that highlights some key comparisons:
| Feature | QFT Plus | TST |
|---|---|---|
| Method | Blood Test | Skin Test |
| Number of Visits | One | Two |
| Affected by BCG Vaccination? | No | Yes |
| Reading Results | Objective, lab-based | Subjective, visual assessment |
Navigating TB Testing: Talking to Your Doctor
The information in this post is intended for educational purposes and should not be taken as a substitute for advice from a qualified medical professional. Any medical decisions should be made after a comprehensive discussion between you and your doctor, who can provide personalized guidance based on your specific health history, circumstances, and concerns. A key factor for those considering the qft test is that a recent mRNA COVID-19 vaccination does not influence the results.
The CDC has issued a statement clarifying that TB tests, like the QFT Plus, can be administered without concern for interference from COVID-19 vaccines.
FAQs About QFT Test
What is a QFT blood test?
The QuantiFERON-TB Gold (QFT) test is a blood test that checks for infection with tuberculosis (TB) bacteria. Unlike the tuberculin skin test, this option involves a blood draw instead of injecting anything under your skin. It detects an immune response by measuring how many infection-fighting cells, specifically interferon-gamma-producing T-cells, are triggered by the test’s antigens. The QFT test can identify exposure to the bacteria, but it doesn’t differentiate between latent infection and active disease, so your doctor will make further assessments if needed. These might include a review of your medical history, a physical examination, or additional diagnostic tests.
What does it mean if I have a positive QuantiFERON test?
A positive QuantiFERON test doesn’t necessarily mean you are actively ill with TB. Instead, it indicates that you’ve been infected with the TB bacteria at some point. Your doctor will likely recommend more tests, like a chest x-ray and a sputum sample examination to see if you have an active TB infection. This helps determine if the bacteria are currently active and causing disease.
What is the difference between a TB test and QuantiFERON?
A TB test can refer to either the TST skin test or a blood test like QuantiFERON, also known as an IGRA test (Interferon Gamma Release Assay). Both aim to identify exposure to TB, but they have several differences. A TST test requires two appointments to administer the injection and read the reaction on your skin a few days later, and its results can be affected by BCG vaccination.
On the other hand, a QFT or IGRA test needs just one lab visit to draw a blood sample. Additionally, previous BCG vaccinations do not impact the outcome. Both methods may be used to screen individuals for latent TB infection (LTBI). Healthcare providers consider various factors, such as the patient’s medical history and risk factors, when deciding which test is most appropriate.
What is the gold standard test for TB?
While there isn’t a singular “gold standard” TB test, recent CDC guidelines recommend using either an IGRA blood test like QuantiFERON or a TST for diagnosing latent tuberculosis infection in adults and children 5 years or older. In children under 5, they still recommend a TST, though they do note some experts use blood tests for them too. This guidance highlights the rising prominence of IGRA blood tests in TB screening, recognizing their comparable accuracy and ease compared to the more traditional TST method.
For those specifically interested in young children’s treatment, you might find helpful information in the American Academy of Pediatrics (AAP) guidance1 on blood tests.
Conclusion
While receiving a recommendation for a qft test might initially seem concerning, remember this test is a helpful tool for detecting possible TB exposure early. Having a deeper understanding of this test can reduce any anxieties and enable you to proactively engage in conversations with your doctor. Keep in mind that a healthcare professional will evaluate your overall situation for informed decisions about further evaluation and treatment.
