QuantiFERON®-TB Gold Plus 1 Tube

QuantiFERON®-TB Gold Plus, 1 Tube Test for Tuberculosis Detection

Also Known As: QFT-Plus, QFT, TB blood test, QuantiFERON®-TB Gold test, Tb test

What is the QuantiFERON®-TB Gold Plus, 1 Tube Test?

The QuantiFERON®-TB Gold Plus, 1 Tube test, often abbreviated as QFT-Plus, is an advanced blood test designed to detect whether an individual has been infected with Mycobacterium tuberculosis, the bacterium responsible for tuberculosis (TB). This tb test is particularly innovative as it requires just one blood draw, thereby simplifying the testing process compared to the traditional tuberculin skin test (TST), also known as the PPD test (tb skin test) . The Tb skin test requires a person to return to the healthcare provider 48-72 hours after the initial injection to have their skin reaction read, which can be a significant inconvenience and sometimes leads to people not completing the test. The QFT-Plus, on the other hand, eliminates the need for a return visit.

The QuantiFERON®-TB Gold Plus test works by mixing blood from the patient with synthetic peptides that simulate the TB antigens. These antigens are proteins associated with the TB bacterium. If the patient's immune system has been primed by a prior TB infection, their white blood cells will remember these antigens and react by releasing a signaling protein called interferon-gamma (IFN-γ). This reaction happens within the specialized testing vial itself. Once the blood is drawn and mixed with the antigens, it's incubated for a period to allow for any potential immune response. Afterward, the sample is tested to measure the amount of IFN-γ that has been produced. An elevated level of IFN-γ typically indicates that the person's immune system has responded to the TB antigens, revealing a current or past infection.

Traditional TB skin tests can sometimes give false-positive results, particularly in individuals who have been vaccinated with the BCG vaccine or who have sensitivities to non-TB mycobacteria. The QFT-Plus test is more specific to TB and is not affected by prior BCG vaccination, which makes it a more accurate option in many cases.

It's important to note that while the QuantiFERON®-TB Gold Plus test is an excellent tool for detecting latent TB infection, it cannot differentiate between latent and active tuberculosis. Individuals who test positive will usually require additional investigations, such as a chest X-ray or sputum sample, to determine whether the TB infection is active and requires treatment.

What is QuantiFERON®-TB Gold Plus Test Used For?

 The QuantiFERON®-TB Gold Plus, 1 Tube test primarily serves a crucial role in the diagnosis of latent tuberculosis infection (LTBI). To understand the significance of this test, it's essential to differentiate between active TB disease and LTBI.

Latent TB Infection (LTBI) is a condition where an individual is infected with Mycobacterium tuberculosis, but the bacteria remain inactive and present no symptoms. People with LTBI are not contagious, meaning they cannot spread TB bacteria to others. However, LTBI is a concern because it can potentially progress to active TB disease, especially if an individual's immune system becomes weakened.

Active TB disease, on the other hand, is when the bacteria are multiplying and causing symptoms, such as a chronic cough, chest pain, fever, and weight loss. Active TB is contagious and can be spread to others through airborne particles from an infected person's coughs or sneezes.

The utility of the QuantiFERON®-TB Gold Plus test lies in its ability to identify those with LTBI before they develop active disease. Detecting LTBI is essential for several reasons:

• Preventing the Spread of TB: By identifying individuals with LTBI, public health officials can ensure that those at risk of progressing to active TB obtain preventive treatment, thereby reducing the risk of a wider outbreak.
• Targeted Treatment: Not every person with LTBI will progress to active TB disease. Treatment recommendations, including the use of antibiotics, can be targeted to those individuals who are at a higher risk — such as people with weakened immune systems including those with HIV/AIDS, diabetes, or those receiving immunosuppressive therapy.
• Individual Health Monitoring: Knowing that someone has LTBI allows for ongoing monitoring of their health status. Should any symptoms arise that suggest a transition from latent to active TB, immediate action can be taken.
• Occupational Health and Safety: In certain jobs, particularly healthcare, where workers are at a higher risk of being exposed to TB, regular screening with tests like the QuantiFERON®-TB Gold Plus can be vital in ensuring a healthy working environment.
• Public Health Management: In countries with low to moderate incidences of TB, identifying and treating LTBI can be a critical component of TB elimination strategies.

Given these important reasons, individuals who are at an increased risk for TB infection or reactivation of latent TB, such as recent contacts of TB patients, immigrants from TB-endemic regions, residents of high-risk congregate settings (like prisons or nursing homes), healthcare workers, and immunocompromised persons, may be recommended by healthcare providers to undergo screening with the QFT-Plus test. The QuantiFERON®-TB Gold Plus test thus acts as a proactive measure in the management of TB. By providing a means for early detection of LTBI, it aids in the prevention of active TB disease, thereby potentially saving lives and preventing new infections.

Why and When Do You Need to Get Tested For TB Infection?

Tuberculosis testing is a preventive health measure crucial for individuals who may be at an increased risk of being infected with TB. The QuantiFERON®-TB Gold Plus test is often recommended in the following circumstances:

High-Risk Groups: Certain individuals are more likely to be exposed to Mycobacterium tuberculosis or to progress from latent to active TB due to factors that compromise their immunity or increase their exposure risks. These high-risk groups include:

• People with HIV/AIDS: TB is a leading cause of illness and death for those who are HIV-positive because their immune system's ability to fight TB is weakened.
• Close Contacts of TB Patients: If someone in your household or someone you work or live closely with has been diagnosed with active TB, you have a higher chance of being infected.
• Healthcare Workers: Medical professionals who treat or come into contact with individuals with TB are at an elevated risk, making regular TB testing vital for disease control.
• Residents of Countries with High TB Rates: If you have moved from or lived in a region where TB is prevalent, testing is usually encouraged since there's a greater likelihood of exposure.
• People Who Use Tobacco or Substances: Those who smoke, use illicit drugs, or abuse alcohol are at a higher risk for TB infection and disease progression.
• Immune-compromised Individuals: People with conditions or treatments that weaken the immune system, such as diabetes, chronic renal failure, certain cancers, or those who are undergoing immunosuppressive therapies like corticosteroids or TNF inhibitors, are more susceptible to TB.

Symptoms Indicating TB: You should consider being tested for TB if you exhibit symptoms typically associated with active TB disease. These include:

• Persistent Cough: A cough lasting three weeks or longer that may produce sputum and at times, blood.
• Weight Loss and Lack of Appetite: Unexplained weight loss and a disinterest in food which can be signs of a TB infection.
• Fever: Often low-grade and potentially accompanied by chills and night sweats.
• Fatigue and Weakness: A general sense of feeling tired or weak which doesn't seem to improve with rest.
• Chest Pain: Pain with breathing or coughing.
• Swollen Lymph Nodes: Particularly in the neck area.

Preventive Care: Beyond symptomatic cases and high-risk groups, TB testing may be a requirement or recommendation for:

• Pre-Employment Screening: In certain occupations, especially in healthcare settings, educational institutions, and correctional facilities.
• Immigration Purposes: People seeking permanent residence in some countries may need to be tested as part of a medical examination.
• Before Starting Immunosuppressive Therapy: Testing is advised since such treatments can trigger the reactivation of latent TB.

Comprehensive TB testing with QuantiFERON®-TB Gold Plus is an essential component of a public health approach to this global health concern, ensuring that at-risk individuals are identified and can receive appropriate care and treatment. If your personal health history or current circumstances align with any of the above situations, you may benefit from a discussion with your healthcare provider about TB testing.

Which Kind of Sample is Required for the QuantiFERON®-TB Gold Plus test?

To conduct the QuantiFERON®-TB Gold Plus test, a blood sample is required. This sample is typically drawn by a healthcare professional using a needle inserted into a vein in your arm,  which is the standard method for collecting blood samples for a wide array of laboratory tests.

Here's what you need to know about the sample collection for the QuantiFERON®-TB Gold Plus test:

Sample Collection:

• The process is generally quick and may cause mild discomfort, similar to any regular blood test.
• A clinical staff member will draw a small amount of blood into a specialized QuantiFERON® blood collection tube.
• The blood draw can be done at a doctor’s office, a lab, or a designated clinic.

Post-Collection Processing: Once the blood sample is taken, it's crucial for it to be processed according to the specific protocol of the test. This usually means that the blood must be kept at a certain temperature and needs to be sent to the laboratory for analysis within a specified time frame. This is because the accuracy of the test results can be affected if the blood cells deteriorate or are not handled correctly.

Do You Need to Prepare for the QuantiFERON®-TB Gold Plus Test?

Here's a simple guide on how to prepare for the QuantiFERON®-TB Gold Plus test:

• Dietary Restrictions: One of the advantages of the QuantiFERON®-TB Gold Plus test is that there are no dietary restrictions. You are allowed to eat and drink as you normally would prior to the test. There's no requirement to fast or avoid certain types of food or beverages.
• Daily Activities: There are also no special instructions regarding alterations to your routine activities. You can continue with your day-to-day tasks without the need to modify your schedule around the test.

• Medications: In most cases, you can also continue taking your medications as prescribed. However, it is always a good idea to inform your healthcare provider about any medications or supplements you're taking, as they will let you know if any could potentially interfere with the test results.

Before the Test:

• Wear clothing with sleeves that can easily be rolled up to facilitate the blood draw.
• Stay hydrated before the test. Being well-hydrated can sometimes make the blood draw easier.
• It's advisable to let the healthcare professional know if you have any conditions that could affect the blood draw, such as a bleeding disorder or a fear of needles.

After the Test:  

No special precautions are needed. You can resume your normal activities immediately after the sample is taken.

If your healthcare provider has not specified any special instructions, you can proceed with the test without any significant preparations or disruptions to your daily life.

What is Being Tested in Particular in QuantiFERON®-TB Gold Plus test?

The QuantiFERON®-TB Gold Plus test delves into the complex workings of your immune system to detect tuberculosis infection. At the core of this test are two particular sets of TB antigens: peptides simulating the proteins ESAT-6 and CFP-10, which are found in Mycobacterium tuberculosis but not in Bacille Calmette-Guérin (BCG)-vaccinated individuals or most non-tuberculosis bacteria. This specificity is what gives the QFT-Plus test its accuracy and reliability.

Here’s how the test zeros in on these immune responses:

• Immune Response Activation: When the blood sample is mixed with the TB-specific antigens in the test tubes, it essentially recreates a scenario as if the TB bacteria were present in the body. The immune system, particularly the T-cells, will recognize these antigens if there has been a prior infection.
• Interferon-Gamma (IFN-γ) Release: The key to the test is the release of interferon-gamma (IFN-γ), a type of cytokine or signaling protein. IFN-γ plays an important role in the immune system, particularly in its response to infections like TB. If the T-cells in your blood sample react to these TB antigens, they'll release IFN-γ as part of this immune response.
• Measurement and Interpretation: The amount of IFN-γ released in response to the antigens is measured. If an elevated level is detected, it suggests that the immune system has been 'sensitized' to the TB bacteria, indicative of a latent, or possibly active, tuberculosis infection.

It's important to underline that the QFT-Plus test does not directly detect the bacterium itself; instead, it detects the immune system's response to it. Therefore, while a positive reaction indicates that the immune system has encountered the bacteria at some point, it does not distinguish whether the disease is active or latent. This differentiation requires further medical evaluation, typically involving a clinical assessment, radiology, and microbiological studies.

The QuantiFERON®-TB Gold Plus test is therefore an indirect but highly specific marker of TB infection, playing a key part in screening programs, especially for individuals who are at a higher risk of TB or those who have a higher likelihood of progression to active disease if infected. Whether an individual's immune system has encountered TB is a vital piece of the puzzle for healthcare providers working to diagnose, treat, and manage tuberculosis globally.

What Does the QuantiFERON®-TB Gold Plus Test Result Mean?

Interpreting the results from the QuantiFERON®-TB Gold Plus test is a crucial step toward proper tuberculosis management. Here’s what each type of result generally means:

Positive Result: If your test result is positive, it suggests that your immune system has recognized and reacted to the TB antigens introduced during the test. This typically means that you have been infected with the bacterium that causes TB, which may either be in its latent form or active. However, a positive result does not reveal the extent of the infection — whether it's latent or active. This determination requires further medical testing and evaluation. Your healthcare provider may recommend additional tests such as:

• Chest X-ray or CT Scan: These imaging tests help visualize the lungs and check for the presence of TB-related abnormalities that suggest active disease.
• Sputum Test: If pulmonary TB is suspected, you may be asked to provide a sample of mucus from the lungs (sputum) to look for TB bacteria under a microscope or through culture testing.

Negative Result: A negative result implies that there was no detectable immune response to the TB antigens. This generally indicates that it's unlikely you have a TB infection. However, certain factors, such as recent exposure to the bacterium, a compromised immune system, or very early infection, might lead to a false-negative result. Therefore, if TB exposure is highly suspected, the healthcare provider might recommend a repeat test or additional monitoring.

Indeterminate or Inconclusive Result: Sometimes, the test result may not be clear-cut; it's neither positive nor negative. This indeterminate or inconclusive result could occur for a variety of reasons, such as a problem with the blood sample, a lab error, or because the person’s immune system didn't respond to the test as expected, which can happen with immune system disorders. In such cases, your healthcare provider may consider retesting with the same TB blood test, using an alternate test like the TB skin test, or employing additional diagnostic methods to clarify your TB infection status.

Follow-Up Actions: As with any medical test, the QuantiFERON®-TB Gold Plus results should be interpreted within the context of your complete medical history, risk factors, and any symptoms you may have. A positive TB blood test will often trigger a comprehensive clinical evaluation to inform the next steps, which might involve:

• Treatment: If latent TB is confirmed, you may be prescribed antibiotics to prevent the infection from becoming active.
• Isolation Precautions: If active TB disease is diagnosed, especially in the lungs or throat, isolation measures may be initiated to prevent spreading the disease to others.
• Public Health Reporting: Active TB cases are typically reported to public health authorities to monitor and control TB outbreaks.

Understanding your test results can empower you with knowledge about your health condition. Should you test positive for TB, remember that both latent and active TB can be treated successfully with proper medical care. If you receive a negative test result, and if TB risk factors persist, periodic testing may be recommended as a precaution. Always consult with your healthcare provider for the most accurate interpretation of your test results and the appropriate follow-up actions.

Conclusion

The QuantiFERON®-TB Gold Plus, 1 Tube test represents significant progress in Tuberculosis diagnosis, offering a convenient and reliable option for individuals who are at risk for this infection. With TB affecting millions worldwide, accurate and early detection is key to effective treatment and control.  Remember that TB is an entirely preventable and treatable condition when caught early, and tests like the QuantiFERON®-TB Gold Plus play a vital role in halting its spread and ensuring public health. If you think you may be at risk for TB infection, consult with your healthcare provider about getting tested.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr. Tayyab Saeed Akhter on January 12^th, 2024.