To the Editors:
Immunocompromised patients with various causes and degrees of immunodeficiencies, such as stem cell and solid organ transplant recipients, patients with autoimmune diseases, patients with chronic renal failure or HIV-positive patients, are at increased risk of progression from latent Mycobacterium tuberculosis infection to active disease. Therefore, screening for latent tuberculosis and preventive treatment is recommended in this patient population. Tuberculosis-specific interferon (IFN)-γ release assays (TIGRAs) lacking cross-reactivity with Mycobacterium bovis bacille Calmette-Guérin have been introduced into the routine diagnosis of latent tuberculosis infection (LTBI) in the last few years as a more specific alternative to tuberculin skin test (TST). More recent results implicate that QuantiFERON®-TB Gold in tube (QFT-G-IT; Cellestis, Carnegie, Australia) may better predict progression from latent to active disease compared with TST 1, 2.
TIGRAs using stimulation of T-cells with phytohemagglutinin (PHA) as a positive control for identification of false negatives and the classification of indeterminate results may be a better alternative for the prediction of LTBI in immunocompromised patients where IFN-γ release may be affected by immunosuppression. The growing list of data existing on reliability of TIGRAs in immunocompromised patients show that the prevalence of indeterminate results may vary depending on the degree of immunosuppression and the TIGRA test used 3. In addition, PHA and recall antigens use different IFN-γ secretion pathways 4, which may be differentially affected by immunosuppressive conditions. Thus, an in-depth analysis of factors influencing PHA-associated IFN-γ secretion is important for the assessment of TIGRAs in immunocompromised patients. Since disease group dependent and independent risk factors of indeterminate results in immunocompromised patients have not been evaluated prospectively using the third generation QFT-G-IT test, we tested QFT-G-IT in patients with diverse conditions of immunosuppression to determine the rate of and identify risk factors for indeterminate results.
After approval of …
