Abstract
Resumo A deteccao precisa da infeccao latente por tuberculose esta se tornando cada vez mais importante devido ao aumento do uso de medicamentos imunossupressores e da epidemia do virus da imunodeficiencia humana, o que aumentou o risco de reativacao a tuberculose ativa (TB). O Teste IGRA QuantiFERON® TB Gold apresenta vantagens frente ao teste de PPD como por exemplo, requer somente uma coleta de amostra sanguinea ; nao ha necessidade que o paciente retorne ao laboratorio para leitura e interpretacao dos resultados; Os resultados sao objetivos, nao requerem interpretacao do leitor ou interferencia de criterios subjetivos; trata-se de um teste in vitro, portanto nao ha “efeito booster” (potenciacao da reacao tuberculinica); o teste nao e afetado por vacinacao previa por BCG ou infeccao por outras especies de micobacterias. Limitacoes sao descritas, apesar de raras, como reacoes cruzadas deste metodo com infeccoes por algumas especies de micobacterias nao-tuberculosis (incluindo Mycobacterium kansasii, Mycobacterium szulgai e Mycobacterium marinum). Ainda ha poucos dados sobre o teste IGRA em certas populacoes, como por exemplo, em criancas, pacientes imunocomprometidos e mulheres gravidas. Nestes grupos, a interpretacao do teste pode ser dificil e mais estudos se fazem necessarios.
Highlights
According to World Health Organization estimates, onethird of the world’s population is currently infected with microorganisms of the Mycobacterium tuberculosis complex, while most infections remain latent in the immune system of their hosts and may progress to the active form and contagious disease
As the QuantiFERON-TB Gold In-Tube (QTF)-G response is based on the release of IFN-γ by T lymphocytes previously sensitized with M. tuberculosis after exposure to two proteins present on the bacterial cell wall: ESAT-6 and CFP-10, since these antigens are absent in the Bacillus Calmette-Guérin (BCG) and most of the mycobacteria present in the environment, prior exposure to these bacteria and BCG immunization do not induce a positive test result.[8,9]
Meta-analysis studies have concluded that the diagnostic specificity of Interferon Gamma Release Assay (IGRA) for tuberculosis infection (TBL) is greater than 95%, whereas specificity is not affected by BCG vaccination.The PPD has a specificity of 97% in populations not vaccinated by BCG, whereas in populations where BCG is administered the specificity is much lower and variable, depending on the age group vaccinated and the number of doses administered of BCG, and the sensitivity of IGRA is reduced in individuals with HIV infection and children
Summary
According to World Health Organization estimates, onethird of the world’s population is currently infected with microorganisms of the Mycobacterium tuberculosis complex, while most infections remain latent in the immune system of their hosts and may progress to the active form and contagious disease. The test may show low sensitivity, especially in immunocompromised individuals Another important limitation to be mentioned is the patient’s need to return to the laboratory 48 to 72 hours after the application to read the results, which is not always achieved and increases the risk of patients with latent tuberculosis of not being identified in the population.[1-4]. As the QTF-G response is based on the release of IFN-γ by T lymphocytes previously sensitized with M. tuberculosis after exposure to two proteins present on the bacterial cell wall: ESAT-6 and CFP-10, since these antigens are absent in the BCG and most of the mycobacteria present in the environment, prior exposure to these bacteria and BCG immunization do not induce a positive test result.[8,9]. Patient needs to attend only once for the exam (It is not necessary for the patient to return to the laboratory for reading and interpretation of the result)
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