A retrospective analysis of tuberculosis screening by interferon-gamma release assay at National Skin Centre, Singapore
- Author:
Hazel H Oon
;
Lim KS
;
Chong WS
;
Colin CT Theng
;
Tan HH
;
Benson Yeo
- Publication Type:Review
- Keywords:
T-Spot.TB, tuberailin skin test, erythema induratum, Latent TB
- From:Malaysian Journal of Dermatology
2011;27(-):10-10
- CountryMalaysia
- Language:English
-
Abstract:
Objective
The T-Spot.TB is an interferon-gamma release assay (IGRA) which is increasingly used in dermatology as a screen for latent
TB before initiation of biologics and for confirming diagnosis of tuberculids. This study aims to explore its concordance
with tuberculin skin tests (TST) and eventual diagnosis of latent TB.
Study design
This is a retrospective review of all patients in NSC who had a TB T-spot test done between 2008 and 2010. We looked
at the dermatological diagnosis, results of T-Spot.TB and TST, chest radiograph findings, tuberculosis status and treatment
of TB.
Result
51 TB T spot tests were ordered in National Skin Centre between 1 January 2008 and 9 June 2010. 31 tests were for patients
with psoriasis with the intention of initiating biologics; 5 were for patients with suspected tuberculids and tuberculosis
verrucosa cutis; 3 were done as part of work-up for possible erythema nodosum; 3 tests were part of screening for latent
TB in hospital staff and 9 tests were performed for other reasons.
There were a total of 13 patients eventually diagnosed with latent or active TB infection. All of whom had a positive
T-Spot.TB result except for 1 patient with an indeterminate result. On the other hand, out of these 13 patients, only 5
showed a positive TST, 2 had negative TST and 4 patients did not have a TST done.
There were a total of 14 positive T-Spot.TB results for which 12 eventually received antituberculous therapy. All patients
with erythema induratum had a positive test result. Six patients’ T-Spot.TB tests were borderline, indeterminate or could
not be interpreted due to insufficient lymphocyte yield.
Conclusion
Our study shows the utility of T-Spot. TB test in various conditions seen in dermatology clinics in a local setting. We suggest
that the T-spot test can supplant the tuberculin skin test in screening latent TB for psoriasis patients for whom biologics are
intended and in erythema induratum. The high incidence of borderline and indeterminate results should not be ignored.
This should be taken into account when interpreting the IGRA especially if patients are on immunosuppressive therapy.
