An Evaluation of QuantiFERON-TB Gold in-Tube and Immunological Tests for TB Diagnosis in Iraqi Patients

Introduction: Mycobacterium is a genus of Gram-positive bacilli that demonstrates the staining characteristic of acid-fastness. Its most important species, Mycobacterium tuberculosis, is the most common etiologic agent of tuberculosis. Tuberculosis causes ill-health among millions of people each year and ranks as the second leading cause of death from an infectious disease worldwide. Between 2003 and 2012, the TB case detection rate gradually and consistently increased to reach thousands cases in 2012 particularly pulmonary type. Latent tuberculosis infection (LTBI), a non-communicable asymptomatic condition, persists in some, who might develop tuberculosis disease months or years later.

Aims: Tuberculosis is an infectious disease caused by the bacillus Mycobacterium tuberculosis and other related species. It typically affects the lungs (pulmonary TB) but can affect other sites (extra-pulmonary TB). A profusion of articles have been published on the accuracy and uses of interferon-gamma releasing assays for detection of this disease.

Experimental Design: A prospective study.

Place and Duration of Study: This study was done in Kirkuk city between November 2012 to February 2013.

Methodology: The present study included 50 individuals (40 suspected tuberculosis patients and 10 healthy controls). The patient were examined for the presence of TB by using QuantiFERON-TB Gold In-Tube(QFT-GIT) assay, polymerase chain reaction (PCR) and compared them with certain new and routine tests like AFB smear, OnSite TB rapid test, erythrocyte sedimentation rate and chest X-ray.

Results: The present study showed a relation between QFT-GIT and OnSite TB rapid test, and they were positive in 25(86%) at the same time; QFT-GIT positive and OnSite TB rapid test were negative in 4(14%) of patients; QFT-GIT negative and OnSite TB rapid test positive were seen in 5(45%); while QFT-GIT and OnSite TB rapid test were negative in 6(55%) of patients. In the control group only one QFT-GIT positive but it was OnSite TB test negative. 9(100%) of individuals for both tests were negative, 29 were males and 21 were females.

Conclusion: The study highlighted the sensitivity of IGRAs for diagnosis of active TB in combination with the rapid IgM/lgG tests for TB.The QFT assay appeared to be a more specific indicator of latent TB infection than TST. The association with blood groups and vaccination is also significant. Blood group ABO and rhesus typing were found to be the most prevalent in pulmonary TB patients with blood group O +ve. Seroprevalence of Mycobacterium tuberculosis antibodies was relatively high in IgG antibody. QuantiFERON TB Gold in Tube high sensitivity and specificity compared to TST, and requires only one visit. In close contacts which were BCG-vaccinated, the QFT assay appeared to be a more specific indicator of latent TB infection than TST.

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