Diagnostic Efficacy of T-SPOT.TB for Active Tuberculosis in Adult: A Retrospective Study

Abstract

Purpose

To explore the diagnostic efficacy and optimal diagnosis threshold of T-SPOT.TB for active tuberculosis in adults and to evaluate the influential factors for T-SPOT.TB results.

Patients and Methods

A retrospective study of 1193 adult inpatients from April 2015 to March 2018 in Ruijin Hospital was conducted. All included patients underwent T-SPOT.TB assay, and were divided into two groups, active tuberculosis (ATB) and non-active tuberculosis (non-ATB) groups. Their demographic data, underlying diseases, personal history and laboratory findings were collected to calculate the diagnostic efficacy at different diagnosis thresholds and analyze the impact factors. Symptoms and imaging features of ATB patients were recorded and analyzed.

Results

A total of 114 ATB patients and 1079 non-ATB patients were included in the study, and ATB patients had a higher level of T-SPOT.TB than the non-ATB group. Sensitivity and specificity of T-SPOT.TB for diagnosing ATB are 78.95% and 68.58% as the threshold at 6sfu. In the diagnosis accordance curves, ESAT-6, CFP-10, and max (ESAT-6 or CFP-10) reached the plateau at 40sfu, while sum (ESAT-6 and CFP-10) reached the plateau at 70sfu. Multivariate logistic regression analysis showed that obsolescent tuberculosis (p=0.001), smoking history(p=0.005), diabetes(p=0.035) and advanced age (≥65 years old) (p=0.031) were risk factors for false-positive result of T-SPOT.TB. In terms of imaging features, logistic regression analysis suggested that the thin-wall cavitary lesion was the only feature associated with the result of T-SPOT.TB.

Conclusion

As for using T-SPOT.TB test to diagnose active tuberculosis, increased threshold could significantly elevate the diagnosis accordance. And we suggest that the threshold of T-SPOT.TB could be increased to 40sfu for diagnosing ATB. Attention should be paid when diagnose ATB in population with obsolescent tuberculosis, smoking history, diabetes and advanced age, for the risk of false-positive.

Keywords:

• T-SPOT.TB
• active tuberculosis
• diagnosis threshold

Abbreviations

TB, tuberculosis; ATB, active tuberculosis; PTB, pulmonary tuberculosis; MTB, mycobacterium tuberculosis; NTM, nontuberculous mycobacteria; WHO, World Health Organization; BCG, Bacillus Calmette-Guerin; LTBI, latent tuberculosis infection; TST, tuberculin skin test; IGRA, interferon-γ release assay; ELISA, enzyme-linked immunosorbent assay; PBMCs, peripheral blood mononuclear cells; ESAT-6, early secretory antigenic target; CFP-10, culture filtrate protein-10; IFN-γ, Interferon-γ; Th1, Type 1 helper T cell; IL, Interleukin; M, Macrophage; PPV, positive predictive value; NPV, negative predictive value; Se, sensitivity; Sp, specificity; NLR, negative likelihood ratio; PLR, positive likelihood ratio; ROC, receiver operator characteristic; AUC, Area Under the Curve; OR, odds ratio.

Ethics Statement

The study was approved by The Research Ethics Commission of Ruijin Hospital. This study complied with the Declaration of Helsinki. Owing to the retrospective nature of the study, we only reviewed the medical records and all identifiable personal information was removed for privacy protection. So, patient consent for inclusion was waived.

Disclosure

The authors declare that they have no competing interests.

Additional information

Funding

This study was funded by Shanghai Municipal Key Clinical Specialty (shslczdzk02202); Shanghai Key Laboratory of Emergency Prevention, Diagnosis and Treatment of Respiratory Infectious Diseases (20dz2261100); Shanghai Municipal Health Commission (2019SY006); and National Natural Science Foundation of China (81970020, 8217010230).