The Quantiferon test is a special blood test used to detect an infection with tuberculosis bacteria in the body, even when no symptoms are present yet.
What happens during the Quantiferon test?
For this test, a small amount of blood is taken and examined in a laboratory. The aim is to find out whether the immune system has already come into contact with the bacteria that cause tuberculosis. Tuberculosis, often shortened to TB, is an infectious disease that mainly affects the lungs but can also affect other organs. Coming into contact with the bacteria does not always lead to symptoms straight away. Many people carry the bacteria without ever becoming ill. The Quantiferon test helps to find out exactly that: is there a silent, so-called latent infection, or not?
In the laboratory, certain components of the tuberculosis bacteria are added to the blood sample. If the immune system has already been "prepared" for them, it responds by releasing a specific messenger substance called interferon gamma. The amount of this messenger substance is measured, and from this it is determined whether an infection is present.
When is the test used?
The Quantiferon test is used mainly when tuberculosis is suspected, or when it needs to be checked whether someone has been infected with the bacteria without having developed any symptoms yet. This is important, for example, when close contacts of a person with active tuberculosis are being examined, or when medical staff regularly work with high-risk patients.
The test is also recommended before certain medical treatments, such as a planned course of medication that weakens the immune system. This is because an undetected tuberculosis infection could suddenly become active under these conditions and take a serious course.
What does a positive result mean?
A positive test result means that the immune system has already come into contact with tuberculosis bacteria. This can point to an active infection or to one that has been present for some time but is currently dormant. In most cases, what is found is a so-called latent tuberculosis. This means the bacteria are present in the body but are not causing any symptoms and are not being passed on to others.
A positive result alone does not automatically mean that treatment is necessary. A thorough medical assessment always follows, often with further investigations such as a chest X-ray or a physical examination. A targeted course of treatment is only started when there are signs of active tuberculosis.
What should be done with a negative result?
If the Quantiferon test comes back negative, this speaks against an infection with tuberculosis bacteria. It means that no contact with the bacteria has taken place so far, or that the immune system has not responded to it. In rare cases, the result can also be falsely negative, for example if the immune system is weakened or if the infection occurred only very recently. If there is any uncertainty, the test can be repeated after some time.
How reliable is the Quantiferon test?
The Quantiferon test is considered very reliable, especially when compared to older methods such as the tuberculin skin test. It is not affected by a previous vaccination against tuberculosis (BCG vaccination) and therefore usually gives clearer results. Even so, there are limits: in very young children, people with a severely weakened immune system, or in the early stages of an infection, the result may be less meaningful.
Are there any risks or side effects?
The Quantiferon test is a straightforward blood test. The risks are limited to the usual, minimal complications of having blood taken, such as a small bruise at the puncture site. Allergic reactions or other side effects are not known.
What happens after the test?
Depending on the result and the individual situation, the treating doctor decides whether further investigations are needed. If active tuberculosis is suspected, a chest X-ray is usually taken and a sample from the airways may be examined. If a latent infection is found, a discussion takes place about whether preventive treatment makes sense in order to stop the disease from becoming active.
What can be done at home?
After the Quantiferon test, no special behaviour is needed straight away. If there is any uncertainty or questions about the results, speaking with a medical professional will help. Anyone who has been in close contact with a person with active tuberculosis should attend the recommended examinations and watch out for possible symptoms such as a persistent cough, fever, or night sweats.
Tuberculosis has become rare in the United Kingdom but has not disappeared. The Quantiferon test helps to detect infections early and to prevent the disease from being passed on. Anyone who is unsure whether a test is a good idea can speak to their GP at any time.
