Tuberc Respir Dis.  2014 Jan;76(1):23-29.

Interferon-gamma Enzyme-Linked Immunospot Assay in Patients with Tuberculosis and Healthy Adults

• Kim CH
• Kim JY
• Hwang YI
• Lee CY
• Choi JH
• Park YB
• Jang SH
• Woo H
• Kim DG
• Lee MG
• Hyun IG
• Jung KS
• Kim HS

Abstract

BACKGROUND
Interferon-gamma assays based on tuberculosis (TB)-specific antigens have been utilized for diagnosing and ruling out latent TB and active TB, but their utility is still limited for TB incidence countries. The aim of this study is to understand the clinical utility of enzyme-linked immunospot (ELISpot) assays among patients with clinically suspected TB and healthy adults in clinical practices and community-based settings.
METHODS
The ELISpot assays (T SPOT.TB, Oxford Immunotec, UK) were prospectively performed in 202 patients. After excluding those with indeterminate results, 196 were included for analysis: 41 were TB patients, 93 were non-TB patients, and 62 were healthy adults.
RESULTS
The sensitivity and negative predictive values of the T SPOT.TB assays for the diagnosis of TB were 87.8% and 89.1%, respectively, among patients with suspected TB. The agreement between the tuberculin skin test (10-mm cutoff) and the T SPOT.TB assay was 66.1% (kappa=0.335) in all participants and 80.0% (kappa=0.412) in TB patients. Among those without TB (n=155), a past history of TB and fibrotic TB scar on chest X-rays were significant factors that yielded positive T SPOT.TB results. There was a significant difference in the magnitude of T SPOT.TB spot counts between TB patients and non-TB patients or healthy adults.
CONCLUSION
The T SPOT.TB assay appeared to be a useful test for the diagnostic exclusion of TB. A positive result, however, should be cautiously interpreted for potential positives among those without active TB in intermediate TB incidence areas.

Keyword

Enzyme-Linked Immunospot Assay; Interferon-gamma; Tuberculosis

MeSH Terms

Adult*
Cicatrix
Diagnosis
Enzyme-Linked Immunospot Assay*
Humans
Incidence
Interferon-gamma*
Prospective Studies
Skin Tests
Thorax
Tuberculin
Tuberculosis*
Interferon-gamma
Tuberculin

Figure

• 

  Figure 1 Boxplot showing the number of spot-forming cells in subjects with positive T SPOT.TB results. *p<0.001, †p>0.05. TB: tuberculosis.

• 

  Figure 2 Regression analysis of the number of spot-forming cells and the size of the induration between the T SPOT.TB assay and the tuberculin skin test.

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