Chemoprophylaxis, when based upon a TST or history of LTBI would be recommended 3X as often than when based on a T-Spot result. T-Spot is highly specific and unlikely to cause false positives. The analysis cannot differentiate between T-Spot insensitivity and TST lack of specificity, although consistent with the literature, TST tends to lack specificity when used in populations with a high prevalence of BCG vaccination. T Spot could be used as annual TB surveillance testing method for HCW. Given the high prevalence of TST+/TSpot–, we recommend TST+ be followed by TSpot for those with BCG histories. More data is needed regarding the concern for conversion/reversion2 rates with serial testing in HCWs. Further studies are warranted about annual cost savings3 and better compliance4 with HCW surveillance while using T Spot testing. REFERENCES TST V/S IGRA We used T Spot as the surveillance test. Retrospective: Mar 2013 – Mar 2014. 6,124 individuals tested. Prior LTBI status in database for 3,478. METHODS RESULTS Background: Currently the CDC recommends that Interferon-Gamma Release Assays (IGRAs) maybe used as an alternative to tuberculin skin tests (TSTs) in the diagnosis of M. tuberculosis infection. IGRAs are typically preferred in persons who have received BCG or with poor rates of returns1. Additional situations where IGRAs may be useful Health Care Workers (HCW) who have been told they have a history of latent tuberculosis (LTBI)), but have declined treatment (in cases of foreignborn HCWs who believe their positive test is a result of BCG). Methods: A retrospective review of HCW IGRA results at Detroit Medical Center (DMC) was conducted from 3/2013 to 3/2014. During the period, 6,138 T-Spot TB test results were obtained (4,631 employees, 343 staff and 1164 commercial clients, contractors, volunteers, students). Epidemiologic data on these HCWs was abstracted and their IGRA results compared with prior diagnosis of LTBI based upon prior TST results or LTBI by history. Results: T-Spot testing revealed 5,801 negative (94.7%), 249 positive (4.1%), and 74 invalid or borderline (1.2%) values. Prior latent TB infection (LTBI) status was known for 3,478. Of these persons, 732 (21.0%) had previously been determined to have LTBI, whereas only 214 (6.2%) tested positive on the T-Spot. When prior TSTs were negative (n=2746), the T-Spot was negative 98.9% of the time. However, when prior LTBI history was positive (n=732), the T-Spot was positive only 25% of the time.