Question 1

How is the QuantiFERON test different from the tuberculin skin test?

Accepted Answer

The QuantiFERON test can be performed during a single visit and does not require a second interpretation visit like the tuberculin skin test. The results are objective, do not require training to interpret, and are not subject to variability in reading methods. The QuantiFERON is also more specific than tuberculin skin testing in individuals who have received the BCG vaccine, as it uses proteins not found in the BCG vaccine.

Question 2

How accurate is the QuantiFERON test?

Accepted Answer

The manufacturer conducted seven sensitivity studies and four specificity studies across multiple sites in the United States, Japan, and Australia. According to a large CDC study, neither the QuantiFERON nor T-SPOT test is sufficiently better than the other, and both require additional follow-up testing in low prevalence populations. When first and second test results are compared, agreement is high with a kappa statistic of 0.84.

Question 3

Can medications or medical conditions affect my test results?

Accepted Answer

The test is not recommended for patients with symptoms of active TB, immunosuppressed patients, or those with diabetes, silicosis, chronic renal failure, leukemia, or lymphoma due to potentially decreased interferon-gamma responses. Conditions that affect immune function, heterophile antibodies, or non-specific interferon-gamma production from inflammatory conditions may affect results. Individuals should discuss their medications and medical history with their healthcare provider before testing.

Question 4

What happens if my test result is borderline or indeterminate?

Accepted Answer

A borderline range (0.20 to 0.99 IU/ml) has been recommended, where follow-up testing is suggested to avoid false-positive or false-negative results near the cutoff. Follow-up tests after initial borderline results were negative in 38.3% of cases without any incident active TB within 2 years, suggesting that more than one-third of those with borderline results are convincingly negative upon retesting. Indeterminate results may require retesting or radiography for confirmation and may cause a potential delay in diagnosis.

Question 5

How long does it take to get my QuantiFERON test results?

Accepted Answer

Test results are typically available in 5-7 days, though some laboratories report results within 2-5 days. The test is time-sensitive and specimens must be received in the laboratory within 14 hours of collection. In some cases, additional time should be allowed for confirmatory or reflex tests, and testing schedules may vary by laboratory.

Question 6

Do I need to do anything special before my blood draw?

Accepted Answer

No special preparation is required for the QuantiFERON test. You do not need to fast or avoid any foods or beverages before the test. Blood collection tubes should be at room temperature at the time of collection, but this is handled by the laboratory staff. You should inform the healthcare provider if you are taking any immunosuppressive medications, as these may affect your immune system's ability to respond to the test antigens.

Tuberculosis (TB) Blood Test (QuantiFERON)