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S.K. Kurup, R. Ursea, J. Tang, W.–K. Lim, H.N. Sen, S. Dahr, R.R. Buggage, R.B. Nussenblatt; Utility of a Gamma Interferon assay as an alternative to PPD TB skin testing in selected patients with intraocular inflammatory disease. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1678.
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Purpose: The Gamma –interferon assay (Quantiferon test), a commercially available in vitro assay against the mycobacterial purified protein derivative(PPD) for the detection of latent tuberculosis(TB),has been recently validated by the Center for Disease Control. We evaluated the utility of this assay to determine the possibilty of latent TB patients with granulomatous uveitis requiring immunosuppressive therapy. Methods:Sera from ten consecutive patients with evidence of active granulomatous uveitis on ophthalmic exam were collected for the Gamma –interferon assay. Possible outcomes for the assay were negative, indeterminate, conditionally positive and positive. Nine of the ten patients were also evaluated with a standard PPD skin test after the specimen for the gamma interferon assay was collected. A positive PPD was defined as an induration 48–72 hours post innoculation according to the standard PPD interpretation. Results:The uveitis was classified anatomically (and clinically) as anterior (1, idiopathic), intermediate (1, idiopathic), posterior (2, idiopathic and ampiginous choroidopathy), panuveitis (4, VKH, Ocular TB, and presumed Sarcoidosis in 2), retinal vasculitis (1, idiopathic) and sclerouveitis (1, idiopathic). The Gamma interferon assay was positive in 5 patients, negative in 4 patients and indeterminate in one patient. Each of the five patients who tested positive also had a positive PPD skin test, including three patients being treated with oral steroids and the patient with ocular TB. Four of the five patients with a positive PPD skin test and positive Gamma interferon assay were immigrants to the United States with a history of childhood BCG( Bacillus Calmette Guerin) vaccination. The PPD skin test was interpreted as negative in the remaining five patients. Conclusion: The Gamma interferon assay may be a useful alternative to PPD skin testing in selected patients with ocular inflammatory disease who need to be screened for latent TB.
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