engleski

Laboratorijska dijagnoza latentne tuberkulozne infekcije

Laboratory diagnosis of latent tuberculosis infection (LTBI) is based on the measurement of the host immune response against Mycobacterium (M.) tuberculosis. The blood test determining interferon-gamma (IFN-γ) released from effector T-lymphocytes (interferon-gamma release assay, IGRA) upon stimulation with M. tuberculosis specific peptides. The differences between two commercially available IGRAs are the type of sample (whole peripheral blood or purified peripheral blood mononuclear cells), the number of specific antigens for ex vivo stimulation and the method for detection of IFN-γ production (the enzyme-linked immunosorbent assay determines IFN-γ concentration and the enzyme-linked immunosorbent spot determines the percentage IFN-γ releasing lymphocyte). The high specificity (about 99%) and sensitivity (65-95%) of IGRAs supports the use of IGRAs in the diagnosis of LTBI in risk individuals but predictive values of IGRAs to predict risk for reactivation of LTBI to active tuberculosis are not known at this moment. The advantage of IGRAs is the possibility of performance quality control. Positive control is used to assess the preanalytical factors as patient's immune status and sample manipulation while negative control offers an insight into the nonspecific IFN-γ level present in the circulation or indicates the presence of interference antibodies in the sample. The unsatisfactory result for control sample is classified as the uninterpretable result of IGRAs. The disadvantage of IGRAs is their inability to distinguish between latent and active tuberculosis infection. The introduction of IGRAs to routine clinical practice has improved the diagnosis of LTBI but each national tuberculose control program should evaluate IGRAs for their own occasion.

latent tuberculosi infection; laboratory medicine

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