Abstract
Recently, the American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention advised against performing the interferon-γ-release assay (IGRA) test for individuals with a low risk of TB, and also recommended retesting low-risk individuals with an initial positive IGRA result. However, to evaluate both sensitivity and specificity of available tests, we compared the performance of the Standard E TB-Feron (TBF) and QuantiFERON-TB Gold Plus (QFT-Plus) assays in healthcare workers (HCWs) and tuberculosis (TB) patients. We also retrospectively investigated diabetes mellitus (DM) comorbidity among the enrolled TB patients. We prospectively collected samples from 177 HCWs and 48 TB patients. The TBF and QFT-Plus tests were performed and analyzed according to the manufacturers’ instructions. We also defined IGRA results between 0.2 and 0.7 IU/mL as ‘borderline’. The agreement rate between TBF and QFT-Plus was 92.0% (207/225) with a Cohen’s kappa value of 0.77 (95% CI, 0.68–0.87). While the majority (26/31, 83.9%) of borderline TBF results were in HCWs, the majority (14/19, 73.7%) of borderline QFT-Plus results were in TB patients. Discordant results were found in 18 samples, with TBF-positive/QFT-Plus-negative or indeterminate results in 11 HCWs and seven TB patients. After resampling from 10 HCWs (seven borderline-positive and three positive results, all <1.0), six reverted to negative. The prevalence of DM comorbidity was very high (35.4%). In summary, TBF showed substantial agreement with the QFT-Plus assay but had a higher positivity rate in both HCWs and TB patients. The negative conversion rate was high (60%) among HCWs whose initial (TB Ag-nil) result was <1.0.
Highlights
Tuberculosis (TB) is a global health problem, with 10.0 million new cases of TB and 1.2 million TB deaths among non-HIV patients in 2019 [1]
The incidence of TB has been decreasing for decades, the incidence of diabetes mellitus (DM), which increases the risk of developing TB by 2–3-fold and increases the risk of TB treatment failure, relapse, and death, is increasing worldwide [2]
IGRA is more specific for M. tuberculosis infection than the tuberculin skin test (TST) [5], several factors, such as old age, body mass index < 16.0 kg/m2, HIV co-infection, and homozygosity for HLA-DRB1*0701, are known to lower the sensitivity of IGRAs [6]
Summary
Tuberculosis (TB) is a global health problem, with 10.0 million new cases of TB and 1.2 million TB deaths among non-HIV patients in 2019 [1]. An immunoassay that measures the interferon (IFN)-γ response to Mycobacterium tuberculosis-specific antigens (interferon-γ-release assay; IGRA) has been used to diagnose latent tuberculosis infection (LTBI) [1]. IGRA is more specific for M. tuberculosis infection than the tuberculin skin test (TST) [5], several factors, such as old age, body mass index < 16.0 kg/m2, HIV co-infection, and homozygosity for HLA-DRB1*0701, are known to lower the sensitivity of IGRAs [6]. DM is associated with insufficient immune responses due to the impaired performance of immune cells [7]. As a result of this impaired immune cell performance and insufficient IFN-γ response [7], the sensitivity of IGRAs is lower than that of the TST in DM patients with smear-negative tuberculosis [8]. QFT-GIT contains a TB antigen tube, whereas QFT-Plus contains two TB antigen tubes (TB1 and TB2): the TB1 antigen tube contains long peptides derived from ESAT-6 and CFP-10 (TB 7.7, which was included in the previous QFT-GIT version, has been removed) and is designed to induce a specific CD4 T-cell response; the TB2 antigen tube contains the long peptides of TB1 and shorter peptides from ESAT-6 and CFP-10 to detect both CD4 and CD8 T-cell responses
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