DETERMINING THE NEED FOR ADDITIONAL TESTING WITH QUANTIFERON TB GOLD IN PATIENTS WITH POSITIVE TUBERCULIN SKIN TEST AND HISTORY OF BCG VACCINATION

Abstract

SESSION TITLE: Chest Infections Posters SESSION TYPE: Original Investigation Posters PRESENTED ON: October 18-21, 2020 PURPOSE: The tuberculin skin test (TST) has been the traditional method for the diagnosis of latent tuberculosis infection (LTBI) for many years. However recently Quantiferon TB gold (QFT) has become the definitive means of diagnosis of LTBI. However QFT is a more expensive test with needs for special equipment and skilled personnel. The purpose of this study is to determine which patient characteristics in patients with positive TST and previous history of BCG vaccination are associated with positive QFT so that we can eliminate the need for additional QTB testing in this patient population. We hypothesize that in patients with high risk features of TST induration diameter of 20mm and more, recent immigration to the USA, advanced age, country of origin with high endemicity, known exposure to active tuberculosis (TB) and smoking history, a positive TST likely expresses true exposure and less likely represents cross reactivity from positive BCG. METHODS: Retrospective chart review was done on adult patients who were referred to our pulmonary clinic with positive TST from January 2014 until December 2019. Patient data was extracted from medical records. The patients were divided into 2 groups. Group 1 consisted of true positive TST patients who had BCG vaccination and were positive for QFT. Group 2 consisted of false positive TST patients who had BCG vaccination but were negative for QFT. The 2 groups were compared with each other to determine if the high risk features were more prevalent in Group 1 compared to Group 2. RESULTS: In total 76 patients met the criteria for our study. Group 1 had 23 patients and Group 2 had 53 patients. The results showed that Group 1 had a higher prevalence of patients with advanced age (4.2%) compared to Group 2 (3%). Patients with exposure to active TB were more prevalent in Group 1(8.3%) compared to Group 2(5.3). However patients with smoking history were more prevalent in Group 2(11.1%) compared to Group 1(4.2%).The above differences were not statistically significant. Patients with TST induration of 20mm and more were more prevalent in Group 1 (60.9%) compared to Group 1(37.7%).The P value in this category alone was trending towards significance with a value of 0.06. Both Group 1 & 2 had equal distribution of patients with recent immigration (16.7%). Patients from Mexico constituted the single largest number of patients in both Group 1(54.2%) & in Group 2 ( 27.7%). CONCLUSIONS: High risk features of large TST size, recent immigration to USA, advanced age, country of origin with high endemicity, known exposure to active TB patients and smoking history does not indicate that positive TST expresses true exposure. Therefore QFT is still needed for definitive confirmation of LTBI. CLINICAL IMPLICATIONS: QFT is a superior testing study than TST for confirmation of LTBI. Hence patients with positive TST must undergo QFT testing to confirm the diagnosis of LTBI. DISCLOSURES: No relevant relationships by Antony Arumairaj, source=Web Response No relevant relationships by Imnett Habtes, source=Web Response No relevant relationships by Hansang Park, source=Web Response No relevant relationships by Fernando Quesada, source=Web Response