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Performance and Practicality of IGRA in Serial Testing for Latent TB Infection in US Healthcare Workers - A Real World Experience FREE TO VIEW

Manish Joshi*, MD; Thomas Monson, MD; Gail Woods, MD
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Central Arkansas Veterans Healthcare System, Little Rock, AR

Chest. 2012;142(4_MeetingAbstracts):142A. doi:10.1378/chest.1386337
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PRESENTED ON: Sunday, October 21, 2012 at 01:15 PM - 02:45 PM

PURPOSE: To assess Quantiferon Gold In-Tube (QFT) assay feasibility, conversions, and reversions in US healthcare workers (HCWs) and compare it with Tuberculin skin test (TST)

METHODS: We identified a HCW cohort at Central Arkansas Veterans Healthcare System (CAVHS) and presented the performance of QFT for initial LTBI testing at CHEST 2010. We retrospectively followed this cohort and analyzed the serial testing results performed after a period of 1 year. We also compared these QFT results with serial TSTs performed prior to QFT 1 and after QFT 2 tests. QFT was performed as per manufacturer's instructions. QFT Conversions were defined as baseline negative results (IFN-γ values <0.35 IU/ml) which became positive on follow up testing. QFT Reversions were defined as initial positive tests (IFN-γ values ≥0.35 IU/ml) which became negative on follow-up testing. TSTs were performed and interpreted by experienced nurses in CAVHS employee health as per CDC guidelines. TSTconversion was defined as an induration ≥10 mm and an increase of ≥10 mm from baseline value as per CDC guidelines.

RESULTS: Of the total 2303 HCWs, 69 were QFT-positive at baseline and 2 were indeterminate. 31/69 (45%) of these HCWs reverted on repeat testing. 25/31(80.6%) HCWs that reverted had a negative baseline TST. Of the 2232 HCWs with baseline QFT-negative results, 71 (3.2%) converted on repeat testing but only 2 HCWs had concordant TST conversion. A third QFT assay was performed in 41 out of these 71 new converters and 90% (37/41) reverted back to negative.

CONCLUSIONS: 1. The QFT is feasible in a large academic tertiary healthcare setting. 2. The QFT conversion rates were very high (>30 times) compared to the baseline TST conversion rates in our institution in the preceding 5 years. However 90% of those new converters who were retested reverted back on repeat QFT testing, suggesting that they were likely false conversions. 3. QFT has poor performance and reproducibility in serial testing of HCW's in the US considering the high conversion and reversion rates associated with the test.

CLINICAL IMPLICATIONS: 1. Our results suggest caution in interpreting QFT results in the serial testing of HCWs in US. 2. Repeat testing and/or TST is suggested for new converters. 3. Healthcare institutions should consider QFT variability, poor short and long term reproducibility, and cost before implementing the test.

DISCLOSURE: The following authors have nothing to disclose: Manish Joshi, Thomas Monson, Gail Woods

No Product/Research Disclosure Information

Central Arkansas Veterans Healthcare System, Little Rock, AR




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