Quantitative scoring of an interferon-gamma assay for differentiating active from latent tuberculosis.
The aim of this study was to assess the contribution of an interferon-gamma release assay (T-SPOT.TB) to the differentiation of active tuberculosis (TB) from latent TB infection by quantifying spot-forming units (sfu). The investigation was a prospective study of contacts exposed to a case of contagious TB and cases of HIV-negative culture-proven TB referred over a 16-month period. Tuberculin skin tests (TSTs) and T-SPOT.TB were performed in 310 contacts 8-12 weeks after exposure. In subjects with culture-proven TB, T-SPOT.TB was performed within 2 weeks of initiation of treatment. The analysis included all contacts with a positive T-SPOT.TB result and all subjects with TB. TB contacts (n = 127) and cases (n = 58) were included. Mean+/-sd T-SPOT.TB results were 107+/-56 (range 1-207) sfu for TB, 54+/-60 (7-239) sfu for contacts with positive T-SPOT.TB results and a TST induration diameter of >5 mm, and 19+/-27 (7-143) sfu for contacts with positive T-SPOT.TB results and a TST induration diameter of < or =5 mm. By receiver operating characteristic curve analysis, a threshold value of 49.5 sfu showed a sensitivity of 83% and specificity of 74% for distinguishing latent TB infection from TB. Although T-SPOT.TB results were significantly related to disease activity, the test cannot be recommended for the diagnosis of tuberculosis.
Janssens
J-P
JP
Centre Antituberculeux, Hôpital Cantonal Universitaire, 1211, Geneva 14, Switzerland. Jean-Paul.Janssens@hcuge.ch
Roux-Lombard
P
P
Perneger
T
T
Metzger
M
M
Vivien
R
R
Rochat
T
T
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000942:Antigens, Bacterial / Q000737:chemistry; D000995:Antitubercular Agents / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D008297:Male; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D012372:ROC Curve; D011933:Reagent Kits, Diagnostic; D015203:Reproducibility of Results; D012867:Skin / Q000378:metabolism; D014374:Tuberculin Test / Q000379:methods*; D014376:Tuberculosis / Q000175:diagnosis* / Q000473:pathology
D000942:Antigens, Bacterial; D000995:Antitubercular Agents; D011933:Reagent Kits, Diagnostic; D007371:Interferon-gamma