Determining the Need for Additional Testing With Quantiferon Tb Gold in Patients With Positive Tuberculin Skin Test and History of BCG Vaccination

Abstract

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.