Assessment of the use of the Quantiferon-TB gold in-tube assay for the diagnosis of TB infection in Lothian, Scotland
Abstract number: P1840
Seagar A-L., Doig C., McSparron C., Hill A., Laurenson I.
Objectives: The Quantiferon-TB Gold In-tube assay (QTBG; Cellestis) detects IFN-g which is released from patients T-cells in response to M. tuberculosis specific antigens. Unlike the TST, results are unaffected by BCG vaccination and most atypical mycobacteria. We assessed appropriateness of assay use from Lothian area patient data from September 2007 to July 2009.
Methods: Scottish and NICE guidance recommends use of interferon-gamma release assays following a positive or unreliable TST. We do not recommend routine use in diagnosis of active TB infection (ATBI). Clinical information sheets completed at the time of sampling were used to assess whether the patient had ATBI or latent TB infection (LTBI). ATBI was determined if TB symptoms were indicated (e.g. weight loss and fever). LTBI was determined in patients with a positive TST result, travel history or CXR changes. If ATBI or LTBI could not be determined from the sheets then an "unknown" verdict was recorded.
Results: Samples were collected from 104 patients. Samples from 7 patients were unsuitable for QTBG testing. 18 (17.3%) QTBG positive, 68 (65.4%) negative and 11 (10.6%) indeterminate results were obtained. 10% of all specimens received were from patients 5 years of age. 76 of 97 patients (78.3%) tested by QTBG had clinical details recorded on the data sheets. ATBI, LTBI or an "unknown" diagnosis was identified in 35 (36.1%), 46 (47.4%) and 23 (23.7%) of patients respectively. 10 (21.7%) of LTBI cases produced a QTBG positive result and 4 (11.4%) of ATBI cases produced a positive result. 14 of 83 (16.9%) of patients assessed to be at high risk of TB produced a QTBG positive result. 54 (65.1%) of these patients had a positive TST result (9 [16.7%] were QTBG positive). 31 patients had a TB contact (3 [9.7%] QTBG positive). 8 of 15 patients who had an abnormal CXR and 12 of 14 patients with a history of travel or living abroad were investigated for LTBI (3 [37.5%] and 4 [33.3%] were QTBG positive respectively). 2 of 6 immunocompromised patients produced QTBG indeterminate results.
Conclusions: 36.1% of QTBG tests were used in assessment of ATBI generally considered inappropriate as false negatives are well documented. In Lothian, QTBG is not currently being used to support the diagnosis of LTBI for healthcare workers and new entrants. To allow the correct interpretation, advice and audit sufficient clinical information is required with requests.
|Session name:||Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Vienna, Austria, 10 - 13 April 2010|
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