Diagnosis of tuberculosis in immunodeficiency?

Study: Blood test in immunocompromised patients better suited for TB diagnosis than skin test

14/11/2014

Many people are infected with the tuberculosis virus without ever getting tuberculosis. Skin or blood tests can be used to determine if the immune system has already come into contact with the pathogen. However, in people with immune deficiency, such as those infected with HIV, transplanted organ transplants and rheumatic patients, detection using the usual methods is much more unreliable, according to a European study. For immunocompromised patients, however, knowledge about infection with tuberculosis pathogens is particularly important as they have an increased risk of developing tuberculosis.

Diagnosis of latent tuberculosis is difficult in case of immune deficiency
Around one third of the world population has already been infected with Mycobacterium tuberculosis or related mycobacteria. But in the least, the respiratory disease breaks out too. An especially high risk for tuberculosis has immunocompromised people.

In Germany, two diagnostic methods are currently used to determine latent tuberculosis without an outbreak of respiratory disease. So there is the prick test, in which the patient tuberculin - a protein mixture with excitatory components - is injected into the skin. When the patient's immune system has already come into contact with the pathogens, cells that respond to tuberculin have been formed. If this is the case, a noticeable hardening occurs at the injection site after about two days. „However, this does not necessarily mean that the patient has been infected with Mycobacterium tuberculosis, since the tuberculin contains particles that also occur in other mycobacteria, "emphasizes Professor Martina Sester, director of the Institute for Transplantation and Infection Immunology of the Saar University, in an interview with the online edition of „Doctors newspaper“. „In addition, the method is not meaningful in immunocompromised patients. They may be infected, but the immune system is unable to respond. As a result, the test is negative. "

Study to check the validity of skin and blood tests for latent tuberculosis
In addition to the skin test, it is possible to perform two blood tests, so-called interferon-gamma release assays (IGRA). The blood components of the tuberculosis pathogen are added, which occur exclusively in Mycobacterium tuberculosis. To determine the response of the blood cells to the pathogens, the concentration of the immune system protein interferon-gamma is determined. After 24 hours, the result is available. „If the result is positive, the patient is infected, "Sester told the journal.

In a study with more than 1,500 patients from eleven European countries in 17 clinics that Sester coordinated at the Homburg University Hospital, it was now examined to what extent the results of these diagnostic procedures are actually reliable. In addition, the researchers wanted to know whether statements about the disease risk could be made about the test results. The study involved 29 researchers from the tuberculosis network TBNET.

Researchers want to develop more reliable tuberculosis diagnostic procedures for immunocompromised patients
Subjects, including those with organ and stem cell transplants, rheumatic patients, people with HIV, and patients with chronic renal failure had to undergo both the skin test and the blood tests. Over a two-year period, the researchers observed who caused the outbreak of tuberculosis.

As it turned out, the blood tests on the immunocompromised patients were more meaningful than the prick test on the skin. However, according to the researchers, statements on the risk of disease are limited. „25 to 30 percent of patients with rheumatic or renal insufficiency had infection according to the tests. However, there was no tuberculosis at all. "The respiratory disease only broke out in ten HIV-infected and one organ transplant recipients, but in six of them the tests did not show any infection before, but only two of those actually had tuberculosis all tests are positive.

„Among the immunocompromised patients included in this study, tuberculosis was most prevalent in HIV-infected individuals and was difficult to predict with both the skin test and the blood tests“, so the conclusion of the researchers in their study, which in the „American Journal of Respiratory and Critical Care Medicine“ has been published. They now want to devote themselves to the development of improved test procedures that can predict the risk of illness more reliably. (Ag)