PURPOSE: To asess Performance and Practicality of QuantiFERON-TB Gold In-Tube(QFT-GIT)assay for the detection of LTBI in US healthcare workers (HCW)in large healthcare setting.
METHODS: Retrospective chart review of all CAVHS (Central Arkansas VA Healthcare syatem)healthcare workers who underwent QFT-GIT testing as a part of annual employee screening to detect LTBI from 11/08 to 10/09. Protocol was approved by CAVHS IRB. Specific variables collected were QFT-GIT results and prior or concurrent TST (Tuberculin Skin test)Readings. The QFT-GIT test was performed according to the manufacturer’ s instructions(Cellestis Ltd, Carnegie, Australia)with a cutoff value for a positive test of IFN-g of 0.35 IU/ml or greater. Some tests were repeated (positive and indeterminate)and repeat readings were recorded as final readings for indeterminate tests for this study purposes. TST’ s were performed and/or reported in Electronic Medical Records(EMR) of CAVHS. For this study, negative TST was <5mm induration after 48-72hrs of TST placement.
RESULTS: 3290 healthcare workers underwent QFT-GIT testing from 11/08 to 10/09, 3380 tests were performed. 129/3290 were reported positive, 3155 negative and 6 were indeterminate. 45 HCW with positive tests underwent repeat testing, median 2 weeks(range 1-8 weeks)and 18/45 (40%) were reported negative. There was overall good agreement between QFT-GIT and TST(>99%), however positive tests in each category showed huge discordance (>50%).
CONCLUSION: 1. QFT-GIT is feasible in large healtcare setting as an alternate to TST for annual LTBI screening in healthcare workers. 2. The short term reproducibility of positive QFT-GIT tests is poor. 3. There is large discordance among positive tests (TST and QFT-GIT). Superiority/higher predictive value of one test over the other can’ t be estimated as there is no gold standard to detect LTBI.
CLINICAL IMPLICATIONS: 1. Our study suggests that all positive QFT-GIT tests,as a part of annual employee screening in HCW to detect LTBI, upto values of 2 IU/mL should be confirmed by repeat testing. 2. More long term studies are needed to assess long term reproducibility and predictive value.
DISCLOSURE: Manish Joshi, No Financial Disclosure Information; No Product/Research Disclosure Information