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QuantiFERON is a blood test used for the detection of tuberculosis (TB) infection. It is an alternative to the traditional tuberculin skin test (TST), also known as the Mantoux test. QuantiFERON is based on interferon-gamma release assays (IGRAs) and is often referred to as an IGRA test.

The QuantiFERON test measures the immune response of a person's white blood cells to the presence of the bacterium that causes tuberculosis, Mycobacterium tuberculosis. It does this by stimulating a blood sample with specific TB antigens and then measuring the amount of interferon-gamma released in response. Interferon-gamma is a protein that is produced by the immune system when it encounters the TB bacterium.

The advantage of QuantiFERON over the tuberculin skin test is that it doesn't require a person to return for a second visit to have the test results read. The results are also less likely to be influenced by previous TB vaccination (e.g., with the Bacillus Calmette-Guérin or BCG vaccine) and some environmental mycobacteria.

QuantiFERON can be used to help diagnose latent tuberculosis infection (LTBI), which means a person has been infected with TB bacteria but doesn't have active TB disease. It is also used to determine if someone needs treatment to prevent the development of active TB disease. It helps identify individuals at risk of developing active TB in the future.

The QuantiFERON test typically includes TB-specific antigens, such as ESAT-6, CFP-10, and TB7.7. These antigens are not found in the BCG vaccine, which is used to prevent TB, so the test is less likely to give false-positive results in individuals who have been vaccinated with BCG.

The results are reported as International Units per milliliter (IU/mL) of interferon-gamma released in response to the TB antigens. A positive result indicates that the individual has been infected with TB, but it doesn't differentiate between latent and active infection. False-negative and false-positive results can occur.

Latent tuberculosis infection (LTBI)

LTBI refers to a condition where an individual has been infected with the bacteria that cause tuberculosis (Mycobacterium tuberculosis), but they do not have active tuberculosis disease. In other words, the bacteria are present in the body, but they are in an inactive or latent state. People with LTBI do not exhibit any symptoms of TB, and they are not contagious to others.

Key points about LTBI include:

  • No Symptoms: Individuals with LTBI do not feel sick, and they do not experience the typical symptoms of active TB, such as cough, fever, weight loss, and night sweats.
  • Infection Control: Although people with LTBI are not infectious, there is a risk that the infection could become active in the future. Therefore, LTBI is an important consideration for public health and infection control.
  • Risk of Progression: LTBI can progress to active TB disease, especially in individuals with weakened immune systems. This progression can occur at any time, but the risk is highest within the first two years of infection.
  • Testing and Diagnosis: Testing for LTBI is typically done using tests like the tuberculin skin test (Mantoux test) or interferon-gamma release assays (IGRAs), such as QuantiFERON. A positive test result indicates the presence of TB infection.
  • Treatment: Individuals with LTBI may be offered preventive treatment to reduce the risk of the infection progressing to active TB disease. Common medications for LTBI treatment include isoniazid (INH) and rifampin.
  • High-Risk Groups: Certain groups of people are at higher risk of developing active TB from LTBI, including individuals with compromised immune systems (e.g., HIV-positive individuals), recent contacts of active TB cases, and those from regions with a high TB prevalence.

It's important to note that LTBI is a different condition from active tuberculosis. Active TB is characterized by the presence of active disease and symptoms, whereas LTBI represents a latent infection without symptoms. Identifying and treating LTBI is an important public health strategy to prevent the reactivation and spread of tuberculosis.

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