Utilization of interferon gamma release assays (IGRAs) for the detection of latent tuberculosis infection (LTBI) at a tertiary care hospital
Molina-Pallete GM, Kansagra J, and Brar I. Utilization of interferon gamma release assays (IGRAs) for the detection of latent tuberculosis infection (LTBI) at a tertiary care hospital. Am J Respir Crit Care Med 2017; 195:A4004.
Am J Respir Crit Care Med
Rational Tuberculosis infection (TBI) continues to be a striking global public health problem, incident cases exceeded 9.6 million and deaths 1.5 million in 2014. Five to ten percent of people with latent TBI will develop active tuberculosis (TB) at some time during their life. The detection and treatment of LTBI is a key strategy in the control of TB infection. Improved methods for detecting LTBI and TB disease are required. IGRAs incorporate Mycobacterium tuberculosis (MTB) specific antigens representing advances in tuberculosis immunology. At Henry Ford Hospital (HFH) IGRAs have been available since 2010. Methods PATIENT IDENTIFICATION Patients who had IGRAs performed were identified from the microbiology laboratory database and charts were reviewed to collect patient data. INCLUSION/ EXCLUSION CRITERIA All patients that underwent IGRAs testing from January 2010 - June 2011 at HFH. STATISTICAL ANALYSIS Description of the variables was performed using chi-square (or Fisher exact test) as a measure of association. Sensitivity, specificity, NPV and PPV were calculated using the tuberculin skin test (TST) as the gold standard. Results A total of 228 patients underwent IGRAs, 55% were male, 16% had positive IGRAs, and their mean age was 47.9+14.7 years. We stratified the patients in 2 groups, the IGRAs + and IGRAs-. No patient characteristic was significantly different between groups, except for positive HIV status; 58% vs 31% respectively (p=0.004). Of the 228 patients, 53 % (n=122) were HIV positive. Of the 11 HIV positive patients who were IGRAs positive, 7 (64%) had a CD4 > 500, 4 (36%) had a CD4 between 200-349 and no patients had a CD4 of less than 200. A total of 124 patients also had a TST performed, 26% were positive. The sensitivity and specificity of IGRAs were 60% and 87.8% respectively, with a PPV of 62.1% and a NPV of 86.8%. Conclusion IGRAs testing may have a logistical advantage over TST. IGRAs are a valuable screening tool however their result s should not be used alone, as the sensitivity according to our study is 60% using TST as gold standard. Also, its utility in HIV+ needs to be studied further along with stratification according to CD4.