Performance And Influential Factors Of QuantiFERON-TB Gold In-Tube Assay In The Diagnosis Of Active Tuberculosis

Objectives:QuantiFERON-TB Gold in-Tube (QFT-GIT) has been widely used as a newly developed interferon-y release assays for the diagnosis of active tuberculosis due to its convenience in operation and equipment. However, this test hasn’t been used in China, and it remains to be unknown whether the age and immune suppressive treatment as well as anti-tuberculosis treatment will influence the performance of the detection. We conduct this study to compare the performance of QFT-GIT in the diagnosis of active tuberculosis (ATB) among children and adults in an endemic country like China, and to explore the effects of therapy with glucocorticoids and anti-tuberculosis drugs on its value.Methods:A total of 60 children and 212 adults clinically suspected for ATB were recruited and then tested with QFT-GIT. Information of clinical symptoms, pathological findings, imaging presentations and treatment history was collected from each patient. We made a comparison of the diagnostic value in children and adults, as well as analyzing the association between its diagnostic value and pretreatment factors.Results:QFT-GIT had a sensitivity of 83.9%(95%CI 66.3%-94.6%) and a specificity of 88.5%(95%CI 70.2%-96.8%) in the diagnosis of ATB in children, with a positive predictive value (PPV) of 92.9%(95%CI 76.5%-99.1%) and a negative predictive value(NPV) of 82.1%(95%CI 63.1%-93.9%). Compared with those values in children, the sensitivity was 73.7%(95%CI 57.8%-85.2%) and the specificity was 70.4%(95%CI 62.9%-77.0%) in adult patients, while the PPV was 47.5%(95%CI 35.3%-60.0%), NPV was 93.3%(95%CI 87.2%-96.8%). Glucocorticoids made a difference in mitogen-stimulated response in both children and adults (P<0.05). In cases with glucocorticoids pretreatment,25.0% of children got false-negative results and 28.6% of adults presented indeterminate results. In cases pre-treated with anti-tuberculosis drugs,44.4% showed false-negative. It was also founded that the level of IFN-γ stimulated by mitogen was lower in patients with ATB than those without both in children and adults.Conclusions:QFT-GIT showed a better sensitivity and specificity in children than in adults. Treatment with glucocorticoids would impact negatively on the diagnostic value of QFT-GIT for all ages. Anti-tuberculosis treatment could decrease the sensitivity. Therefore, we recommend QFT-GIT to be taken before TB-specific treatment and not to be applied to those with immunosuppressive treatment regardless of age. Quantitative analysis of QFT-GIT could be useful for assessing and monitoring TB-specific and non-specific immunity during conversion of the disease.