Free Guide to QuantiFERON-TB Gold Testing Information

What QuantiFERON-TB Gold Is and How It Works

QuantiFERON-TB Gold (QFT-G) is a blood test used to detect tuberculosis infection in people. Unlike older TB skin tests, this test uses a simple blood draw and measures how a person's immune system responds to tuberculosis antigens—proteins associated with the TB bacterium. The test was first approved by the FDA in 2005 and has become a standard screening tool in many healthcare settings across the United States and worldwide.

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The test works through a process called interferon-gamma release. When a person's blood is exposed to TB antigens in a laboratory setting, their immune cells release a chemical called interferon-gamma if they have been infected with tuberculosis. The lab measures the amount of this chemical to determine whether TB infection is present. The results come back as negative, positive, or indeterminate (unclear), and healthcare providers use these results to guide decisions about treatment and further testing.

QuantiFERON-TB Gold differs from the tuberculin skin test (TST), which has been used since the 1920s. The skin test requires a person to return to a clinic 48 to 72 hours after an injection to have the result read. The blood test, by contrast, can be completed in a single visit, though results take a few days to return from the laboratory. A single blood draw is all that is needed—no follow-up visit is required just to get the result.

The test can distinguish between active TB disease and latent TB infection. Latent TB infection means a person has been exposed to the TB bacterium and carries the infection, but the disease is not currently active and cannot be spread to others. Active TB disease means the infection is progressing and the person may have symptoms and can transmit the disease. However, the QuantiFERON-TB Gold test alone cannot determine whether infection is latent or active—that distinction requires additional clinical evaluation and imaging.

Practical Takeaway: QuantiFERON-TB Gold is a blood test that detects TB infection through immune response measurement. It requires one visit for the blood draw and does not require a return appointment just to read results, making it convenient for many healthcare settings and patients.

Who May Need QuantiFERON-TB Gold Testing

The Centers for Disease Control and Prevention (CDC) recommends TB testing for certain groups of people based on TB transmission risk. Healthcare workers are among those most commonly tested because they work in environments where TB exposure is possible. Long-term care facility residents and staff may also need testing because TB spreads more easily in congregate settings where people live closely together for extended periods.

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People with HIV or AIDS have weakened immune systems and are at much higher risk of developing active TB disease if they have latent TB infection. The CDC recommends TB testing for all people with HIV, regardless of their TB exposure history. Similarly, people taking immunosuppressive medications for conditions like rheumatoid arthritis or Crohn's disease may be tested before starting these medications, as these drugs increase TB risk.

Foreign-born individuals from countries with high TB rates—particularly from Latin America, the Caribbean, Africa, and Asia—are tested more frequently. According to the CDC, in 2022, approximately 86 percent of TB cases in the United States occurred in foreign-born people, even though they represent only about 14 percent of the U.S. population. Contacts of people with active TB disease should also be tested to determine whether exposure resulted in infection.

Incarcerated individuals are tested because correctional facilities can present high TB exposure risk. People experiencing homelessness are tested because living in shelters increases transmission risk. People with substance use disorders are also recommended for testing. Additionally, some healthcare systems perform routine TB screening for all employees during hiring, and occupational health programs may include testing as part of standard workplace screening.

It is important to note that testing recommendations may vary based on individual circumstances and local TB epidemiology. A healthcare provider can discuss whether testing is appropriate for a particular person based on their specific situation, risk factors, and exposure history.

Practical Takeaway: QuantiFERON-TB Gold testing is commonly recommended for healthcare workers, people with HIV, those from high-TB countries, and people in congregate settings. Discussing personal risk factors with a healthcare provider helps determine whether testing is suitable.

The QuantiFERON-TB Gold Testing Process and What to Expect

The testing process begins with a healthcare provider ordering the test, typically at a doctor's office, clinic, occupational health department, or hospital. The patient arrives for an appointment where a phlebotomist or nurse collects blood samples. For QuantiFERON-TB Gold, blood is drawn into special tubes that contain TB antigens and other necessary reagents. The collection uses a standard needle and usually takes just a few minutes, similar to any routine blood draw.

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Most patients experience minimal discomfort during the blood draw. The needle is small, and the amount of blood collected is small—typically only a few milliliters. Patients may feel a brief pinch or slight pressure at the needle insertion site, but this is temporary. People who are anxious about blood draws can inform the healthcare staff beforehand; they can often sit or lie down during the procedure to reduce the risk of fainting.

After the blood is drawn, the tubes are sent to a laboratory, usually within the same day. The laboratory staff incubates the blood samples, allowing immune cells to respond to the TB antigens over a period of hours. The lab then measures interferon-gamma levels using a process called an enzyme-linked immunosorbent assay (ELISA). Results typically come back within two to three business days, though some laboratories may provide results within 24 hours.

There is no special preparation required before the test. Patients do not need to fast, avoid medications, or change their diet. They can eat and drink normally before the appointment and can resume normal activities immediately after the blood draw. There are no side effects from the test itself, though some people may experience minor bruising at the needle site, which typically fades within a few days.

The results are usually reported as negative (no TB infection detected), positive (TB infection detected), or indeterminate (unclear, may need repeat testing). A healthcare provider interprets the results and discusses them with the patient, explaining what the result means for their health and whether further evaluation or treatment is needed.

Practical Takeaway: The QuantiFERON-TB Gold test requires a single blood draw with no special preparation. Results arrive within two to three business days, and patients can resume normal activities immediately after testing.

Understanding Test Results and What They Mean

A negative QuantiFERON-TB Gold result indicates that TB infection was not detected based on the immune response to TB antigens. This typically means the person has not been infected with the tuberculosis bacterium. However, there are important exceptions to understand. People who have been recently exposed to TB may have a negative result if the immune system has not yet developed enough of a response to be detected by the test. The CDC recommends retesting three to eight weeks after known exposure if initial testing is negative.

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A positive result indicates that TB infection is present. The person's immune system has responded to TB antigens in a way that suggests current or past exposure to the tuberculosis bacterium. However, a positive result does not tell whether the infection is latent or active. Latent TB infection means the person carries the TB bacterium but the disease is not currently active and cannot spread to others. Active TB disease means the infection is causing illness, and the person may have symptoms and can transmit the disease to others. A positive QuantiFERON-TB Gold result must be followed by additional clinical evaluation—physical examination, symptom assessment, and imaging tests like chest X-rays—to determine whether active disease is present.

An indeterminate result means the test could not determine whether TB infection is present. This can occur for several reasons: the immune response was too low, quality control issues, or problems with sample handling. Indeterminate results are uncommon, occurring in roughly 1 to 6 percent of tests depending on the population tested. When indeterminate results occur, the test is typically repeated after a few weeks.

Important factors affect test accuracy. People with severely weakened immune systems—such as those with untreated HIV with very low CD4 counts—may have false-negative results because their immune system cannot mount a detectable response. Certain vaccines, medications, and medical conditions can also influence results. A healthcare provider reviews