Diagnostic Utility of Interferon-Gamma Release Assay in Tuberculous Lymphadenitis

Abstract

Objective The aim of this study was to evaluate the diagnostic performance of T-SPOT.TB for tuberculous lymphadenitis.Methods Suspected tuberculous lymphadenitis patients between September 2010 and September 2018 who had both peripheral blood T-SPOT.TB test and lymph node biopsy were retrospective enrolled in this study. The cutoff value of T-SPOT.TB test for peripheral blood was set as 24 SFC/10 6 PBMC according to the testing kits. The gold standard for diagnosis of TBL is combination of tissue culture or acid-fast staining, or histological findings consistent with TBL and clinical or radiological response to anti-TB treatment. Diagnostic efficacy of T-SPOT.TB was evaluated, including sensitivity, specificity, accuracy, predictive values, and likelihood ratio.Results Among 91 patients who met the inclusion criteria, we excluded 8 cases with incomplete clinical information and 6 cases who lost of follow-up. According to the gold standard, there were 37 cases of true TBL (9 confirmed TBL and 28 probable TBL) , 30 cases of true non-TBL, and 10 patients of clinically indeterminate diagnosis which were excluded from the final analysis. T-SPOT.TB tests yielded 43 cases of positive response and 24 cases of negative response by. The sensitivity, specificity, accuracy, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR) and negative likelihood ratio (NLR) of peripheral blood T-SPOT.TB for diagnosing TBL were 89.2%, 66.7%, 79.1%, 76.7%, 83.3%, 2.676 and 0.162, respectively. The number of spot forming cells (SFCs) of T-SPOT.TB were [432(134-1264)/10 6 PBMCs] in TBL patients, higher than that in non-TBL patients [0 (0-30) /10 6 PBMCs] with significant statistical difference (Z=-5.306, P <0.001).Conclusions T-SPOT.TB is a rapid and simple diagnostic test for TBL with a high sensitivity and negative predictive value.