Explanation

QuantiFERON TB test (IGRA): what is measured?

The QuantiFERON test is an IGRA (interferon-gamma release assay). In the laboratory, blood is brought into contact with proteins that only occur in the tuberculosis bacterium. If someone has previously been in contact with the bacterium, immune cells (T cells) react to this by releasing the substance interferon-gamma; at 0.35 IU/ml or more, the test is positive. A previous BCG vaccination and most other mycobacteria do not affect the test.

What can it detect?

Tuberculosis infection (also called latent tuberculosis): infected with the bacterium, but not ill and not contagious
A sign of infection in someone with (suspected) active tuberculosis; the test does not distinguish between infection and disease

Result

What does the result mean?

Positive result

A positive test means that your immune system has at some point been in contact with the tuberculosis bacterium. Usually this is a tuberculosis infection without disease: you then have no symptoms and are not contagious. About 1 in 10 people with an infection later become ill, most often in the first 2 years after infection; with a weakened immune system this chance is greater. The test cannot distinguish between an infection without disease, active tuberculosis and previously treated tuberculosis. Symptoms that go with active tuberculosis are a long-lasting cough, night sweats, weight loss, tiredness and fever.

Negative result

A negative test makes a tuberculosis infection unlikely. The immune response only develops a few weeks after infection; that is why the CPT guideline advises testing at least 8 weeks after the last contact with someone with tuberculosis. A negative test does not rule out active tuberculosis: the test can also be negative with active tuberculosis or with a weakened immune system. An indeterminate result means that the controls in the test did not work properly; the test is then repeated once with new blood.

After an abnormal result

With a positive test, the GP refers to the tuberculosis control department of the GGD (municipal public health service) or to a lung specialist. There, active tuberculosis is ruled out with a consultation, a physical examination and a chest X-ray, and it is discussed whether preventive treatment with medicines is useful. Active tuberculosis is notifiable under the Dutch Public Health Act (group B1); the GGD then starts source and contact tracing if needed.

Reliability

How reliable is the test?

There is no gold standard for a tuberculosis infection. According to the CPT guideline on diagnosing tuberculosis infection, the sensitivity of the QuantiFERON test, measured in people with tuberculosis, is about 78 to 81 percent and the specificity 82 to 99 percent; this specificity is clearly higher than that of the skin test (Mantoux), because BCG vaccination plays no role. The meaning of a positive result depends strongly on the chance of infection: in someone without known contact or risk, the chance of a false-positive result is greater. Results close to the cut-off can switch from positive to negative or vice versa when repeated.

What can affect the result?

In the first 8 weeks after infection, the test can still be negative.
A weakened immune system (for example due to HIV or immunosuppressive medicines) and young age more often give a false-negative or indeterminate result.
When people with a low risk are tested repeatedly, such as in periodic check-ups, positive results and fluctuations around the cut-off occur more often than expected.
The blood must be processed in the laboratory within a fixed time; blood that takes too long to arrive can give an indeterminate result.

Who it is for

Who is the test useful for?

Useful for

Useful after close contact with someone with contagious tuberculosis (at least 8 weeks after the last contact), for people who have lived, worked or traveled for a longer period in a country with a lot of tuberculosis, for healthcare workers at increased risk, and before starting medicines that strongly suppress the immune system, such as TNF-alpha inhibitors. After contact with a patient, the GGD (municipal public health service) usually arranges the testing itself. In people without a risk of infection, testing is not useful, because a positive result is then relatively often false-positive. The test is not suitable for diagnosing or ruling out active tuberculosis.

How common is it?

In 2025, 869 people in the Netherlands were diagnosed with tuberculosis; 82 percent of them were not born in the Netherlands. In the same year, 1,652 tuberculosis infections without disease were reported. Among people from countries where tuberculosis is common, according to the CPT guideline, sometimes more than 15 to 20 in 100 have an old infection; among people born in the Netherlands after 1945, this is low.

RIVM key figures on tuberculosis 2025; CPT guideline on diagnosing tuberculosis infection

Drawbacks and risks

In people with a low risk, a positive result is relatively often false-positive; this can lead to a chest X-ray, worry and sometimes months of preventive treatment with medicines that can cause side effects.
A negative test can give false reassurance if the test was done too soon after a contact or if there are symptoms that fit active tuberculosis.

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