Impact of correcting the lymphocyte count to improve the sensitivity of TB antigen-specific peripheral blood-based quantitative T cell assays (T-SPOT.(®)TB and QFT-GIT)

Performance of Interferon-γ Release Assays in Patients with Mycobacterium kansasii Infection

Objective

To evaluate the performance of interferon-γ release assays (IGRAs) in patients with Mycobacterium kansasii infection.

Methods

Consecutive patients between May 2012 and June 2021 who had positive for mycobacterial cultures and who underwent IGRAs (T-SPOT.TB or QuantiFERON-TB Gold [QFT-G]) were included in the analysis. The IGRA positivity rates among patients with M. kansasii isolates were then calculated. If M. kansasii was identified in at least two sputum samples or in sterile samples, M. kansasii disease was then diagnosed. Otherwise, colonisation was considered.

Results

During the study period, 54 patients with M. kansasii infection underwent T-SPOT.TB (n=48) or QFT-G (n=6) assays. The mean age was 44.1±13.4 years, 85.2% (46/54) were male. Eight patients were diagnosed with M. kansasii disease and another 46 patients were considered to have colonisation. Twenty-four patients (T-SPOT.TB, n=23; QFT-G, n=1) were positive for IGRAs, for an overall rate of 44.4% (24/54; T-SPOT.TB, 47.9% [23/48]; QFT-G, 16.7% [1/6]) for IGRAs, 25.0% (2/8) for M. kansasii disease, and 47.8% (22/46) for colonisation.

Conclusion

Positive IGRA rates were relatively low in patients with M. kansasii infection. More efforts are required to improve the performance of IGRAs in diagnosing M. kansasii infection.

Comparison between the Interferon γ Release Assay-QuantiFERON Gold Plus (QFT-Plus)-and Tuberculin Skin Test (TST) in the Detection of Tuberculosis Infection in Immunocompromised Children

Background

Immunocompromised patients are at a higher risk of having latent tuberculosis infection (LTBI). QuantiFERON-TB Gold Plus (QFT-Plus) has been proven to perform effectively in LTBI detection among immunocompromised adults and can overcome the limitations of the tuberculin skin test (TST). However, the role of QFT-Plus in detecting LTBI in immunocompromised paediatric patients has not been well established. Therefore, the aim of this study was to assess the test agreement between QFT-Plus and the TST in LTBI detection among immunocompromised children.

Method

In this cross-sectional study, we enrolled immunocompromised paediatric patients, aged between 5 and 18 years, who were treated with corticosteroids and/or chemotherapy from June to November 2019. We categorized them into three groups based on the following diseases: hematologic malignancies and nephrological and immunological diseases. We recorded the patient characteristics and QFT-Plus and TST results, in which the positive result of the TST was induration ≥ 5 mm. Within the same group, comparisons between the two tests were performed using the McNemar test, and results were statistically significant for p values of <0.05. The kappa index was used to assess the agreement between the two test results.

Results

Among 71 patients (median age: 11.8 years) who underwent TST and QFT-Plus testing, 52% were females, and 69% had a normal nutritional status. Chemotherapy was the most common treatment modality for hematologic malignancy compared to other immunosuppressive treatments. The total number of patients with positive QFT-Plus and TST results was 11/71 (15.5%) and 4/71 (5.6%), respectively, among whom 3/11 patients had positive results in both tests, and one patient with positive TST results exhibited a discrepancy, as this was not followed by positive QFT-Plus results. QFT-Plus generated more positive results than the TST in immunocompromised children (McNemar, p = 0.039 (p < 0.05)). The diagnostic agreement between the tests was fair (K = 0.345, 95% CI: 0.05–0.745).

Conclusion

QFT-Plus detected LTBI more effectively than the TST in immunocompromised children.

Prospective Comparison of QFT-GIT and T-SPOT.TB Assays for Diagnosis of Active Tuberculosis

T-SPOT.TB and QuantiFERON-TB Gold In-Tube (QFT-GIT) tests, as two commercial blood assays for diagnosing active tuberculosis (ATB), are not yet fully validated. Especially, there are no reports on comparing the efficacy between the two tests in the same population in China. A multicenter, prospective comparison study was undertaken at four hospitals specializing in pulmonary diseases. A total of 746 suspected pulmonary TB were enrolled and categorized, including 185 confirmed TB, 298 probable TB and 263 non-TB. Of 32 patients with indeterminate test results (ITRs), age and underlying disease were associated with the rate of ITRs. Furthermore, the rate of ITRs determined by T-SPOT.TB was lower than QFT-GIT (0.4% vs. 4.3%, P < 0.01). When excluding ITRs, the sensitivities of T-SPOT.TB and QFT-GIT were 85.2% and 84.8%, and specificities of 63.4% and 60.5%, respectively in the diagnosis of ATB. The two assays have an overall agreement of 92.3%, but exhibited a poor linear correlation (r² = 0.086) between the levels of interferon-γ release detected by the different assays. Although having some heterogeneity in detecting interferon-γ release, both the QFT-GIT and T-SPOT.TB demonstrated high concordance in diagnosing ATB. However, neither of them showed suitability in the definitive diagnosis of the disease.