Limited added value of T-SPOT.TB blood test in diagnosing active TB: A prospective bayesian analysis - 02/08/11
, Anthony Ashcroft b , Marc Lipman c , Graham H. Bothamley d 
Corresponding author. Tel.: +44 0776 023 1654; fax: +44 0208 773 1510.Summary |
Objectives |
To determine the diagnostic value of a blood interferon-gamma release assay in suspected active tuberculosis (TB).
Methods |
136 subjects with suspected pulmonary TB (pTB) at a single London centre with intermediate TB incidence, were clinically graded into low (<25%), medium, or high (>75%) likelihood of active pTB and then tested by T-SPOT®.TB assay. The diagnosis was confirmed by culture (n = 33), treatment response (n = 13) or a firm alternative diagnosis (n = 90).
Results |
Overall, the T-SPOT.TB sensitivity was 74% (95% confidence intervals 60–84%), positive predictive value (PPV) 56% (43–68%), negative predictive value (NPV) 83% (71–90%), positive likelihood ratio (PLR) 1.75 and negative likelihood ratio (NLR) 0.45. Results for high pTB likelihood subjects: PPV 100%, NPV 25% (7–60%), PLR >69, NLR 0.31. Results for intermediate pTB likelihood subjects: PPV 67% (41–85%), NPV 88% (65–96%), PLR 2.39, NLR 0.26. Results for low pTB likelihood subjects: PPV 15% (6–34%), NPV 92% (79–97%), PLR 1.23, NLR 0.80. False negatives occurred in 24% of cases of active tuberculosis (4 smear and culture-positive, 3 smear negative and culture-positive, and 4 culture negative).
Conclusions |
The predictive values and likelihood ratios show the T-SPOT.TB test does not assist in confidently confirming or excluding active TB, regardless of the pre-test probability of disease.
Le texte complet de cet article est disponible en PDF.Keywords : Bayes’ theorem, Diagnosis, Interferon-gamma release assay, Likelihood ratio, Tuberculosis
Plan
Vol 62 - N° 6
P. 456-461 - juin 2011 Retour au numéro
Article précédent
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