Evaluation of ALS assay of TB-SA for diagnosis of pulmonary tuberculosis

Our plain-English summary of Evaluation of ALS assay of TB-SA for diagnosis of pulmonary tuberculosis, by J. Jiao, M.S. Wang, X.G. Yang, et al (Journal of Immunoassay & Immunochemistry, 2015).

The study

• Authors: J. Jiao, M.S. Wang, X.G. Yang, X.F. Wang
• Journal: Journal of Immunoassay & Immunochemistry
• Published: 2015;36(2):119-27
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The study evaluated tuberculosis specific antigen (TB-SA) antibody in lymphocyte supernatant (ALS) assay for diagnosis of pulmonary tuberculosis (PTB). The mean concentration of TB-SA ALS in PTB patients was significantly higher than that of two control groups (non-PTB patients and healthy subjects, P < 0.001). The area under the curve of the ALS assay were 0.960 (0.904-0.988, PTB vs healthy subjects), and were 0.822 (0.739-0.887, PTB vs Non-PTB patients), respectively. Our data indicated the ALS assay for TB-SA can be used as a screening test and is a useful adjunct to current tests for diagnosis of PTB.

In plain English

This article concerns tuberculosis, not asbestos. The authors, at Shandong Provincial Chest Hospital, China, evaluated the TB-SA 'antibody in lymphocyte supernatant' (ALS) blood test for pulmonary tuberculosis from 2012 to 2013. They tested 62 culture-confirmed tuberculosis patients, 53 patients with other diseases (2 with pleural mesothelioma) and 47 healthy subjects. Antibody levels were higher in tuberculosis patients than in both other groups (p less than 0.001). Against healthy subjects, the area under the curve was 0.960 (95% CI 0.904 to 0.988); at cutoff 0.066, sensitivity was 96.8% (95% CI 88.8 to 99.5%) and specificity 85.1% (95% CI 71.7 to 93.8%). Against other patients, the area was 0.822 (95% CI 0.739 to 0.887); at cutoff 0.167, sensitivity was 67.7% (95% CI 54.7 to 79.1%) and specificity 92.5% (95% CI 81.8 to 97.9%). Sensitivity was 97.7% in smear-positive and 94.7% in smear-negative patients against healthy subjects, but 81.8% and 33.3% against other patients. The authors concluded it can serve for screening and as an adjunct to current tests. They called both measures higher against healthy subjects, though specificity was lower there.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Diagnostic test evaluation at one hospital, from September 2012 to October 2013. Culture-confirmed pulmonary tuberculosis patients were compared with two control groups: non-tuberculosis patients and healthy subjects.
• Who was studied: The study included 62 culture-confirmed pulmonary tuberculosis patients, 53 non-tuberculosis patients and 47 healthy subjects at Shandong Provincial Chest Hospital, Jinan City, China. The non-tuberculosis patients had cancer (21: 19 lung cancer and 2 pleural mesothelioma), pneumonia (8), pleurisy (6), chronic obstructive pulmonary disease (6), bronchiectasis (4) or other diseases (8).
• Exposure: No asbestos or other fiber exposure was studied. The article evaluated a laboratory test that measures IgG antibodies against the tuberculosis antigen TB-SA in fluid from cultured blood lymphocytes (the ALS assay).
• Main results:
  • Mean TB-SA IgG titers (OD450nm) were 0.708 plus or minus 0.688 in pulmonary TB patients, 0.116 plus or minus 0.079 in non-TB patients and 0.042 plus or minus 0.048 in healthy subjects. Titers in TB patients were significantly higher than in both control groups (p less than 0.001).
  • Pulmonary TB patients versus healthy subjects: area under the curve 0.960 (95% CI 0.904 to 0.988). At a cutoff of 0.066, sensitivity was 96.8% (95% CI 88.8 to 99.5%) and specificity was 85.1% (95% CI 71.7 to 93.8%). The positive likelihood ratio was 6.50 and the negative likelihood ratio was 0.04.
  • Pulmonary TB patients versus non-TB patients: area under the curve 0.822 (95% CI 0.739 to 0.887). At a cutoff of 0.167, sensitivity was 67.7% (95% CI 54.7 to 79.1%) and specificity was 92.5% (95% CI 81.8 to 97.9%). The positive likelihood ratio was 8.98 and the negative likelihood ratio was 0.35.
  • IgG levels were significantly higher in sputum smear-positive TB patients (0.925 plus or minus 0.698) than in smear-negative TB patients (0.216 plus or minus 0.324; p less than 0.001). Against non-TB patients (cutoff 0.167), sensitivity was 81.8% in smear-positive patients and 33.3% in smear-negative patients. Against healthy subjects (cutoff 0.066), it was 97.7% and 94.7% respectively.
• The authors' conclusion: The authors concluded that the ALS assay for TB-SA can be used as a screening test for TB. They also concluded that it is a useful adjunct to current tests for diagnosing pulmonary TB, with results within 3 days.
• Limitations the authors state:
  • The authors wrote that sensitivity and specificity were substantially higher when healthy subjects, rather than non-TB patients, were used as controls. They said no explanation has yet been given for this, and that the cause of the difference in IgG titer between these groups needs to be determined. Their own reported specificity was in fact lower against healthy subjects (85.1%) than against non-TB patients (92.5%).

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