Influential Factors of the Indeterminate Results Tested by QuantiFERON-TB Gold In-Tube (QFT-IT) Assay for Diagnosing TB Infection in HIV-Infected Patients.

Background: QuantiFERON-TB Gold In-Tube test (QFT-IT) is a recommended method for diagnosing TB in HIV-infected patients. However, the rate of indeterminate results is higher than that in HIV-uninfected patients. Our previous study showed that the CD4 cell count was an important influential factor for the indeterminate results of QFT-IT. Whether other influential factors affect the QFT-IT results was unclear. Methods: In this paper, 98 HIV-infected patients with suspected TB infection were enrolled and the plasma of peripheral blood was collected for QFT-IT. The relationship between the CD4 T-cell count, lymphocyte count, lymphocyte percentage, and the results of QFT-IT were analyzed. Results: All patients who have the clinical symptoms of TB including fever and productive cough and were later confirmed by other assays including the sputum culture and chest radiography (n = 8) tested as QFT-positive (positive rate 100%). The other 90 patients without clinical symptoms tested as negative (n = 51), indeterminate (n = 33), and positive (n = 6). The lymphocyte count and the lymphocyte percentage as well as the CD4 T-cell count were significant higher in the positive group and negative group than in the indeterminate group (p < 0.05, for all). Conclusions: The QFT-IT could be a potential, simple, and feasible method for diagnosing and screening TB in HIV-infected patients. In addition, the CD4 T-cell count, the lymphocyte count, and the lymphocyte percentage were influential factors of the indeterminate results of QFT-IT.