Tuberculin skin test and predictive host factors for false-negative results in patients with pulmonary and extrapulmonary tuberculosis

Introduction: Tuberculin skin test (TST) has been the standard test for screening for Mycobacterium tuberculosis infection for decades. Identifying persons with latent tuberculosis infection (LTBI) is crucial, as they constitute a reservoir that sustains the global tuberculosis (TB) epidemic. However, different factors, such as HIV infection, can lower the sensitivity of the test. Objectives: The aim of this study was to determine the TST sensitivity in active TB patients and to ascertain risk factors that could be associated with false-negative results. Methods: Retrospective cohort study of all active TB notifications with a TST result (n = 8833), from 2008 to 2015. TST results were interpreted using a 5 mm and 10 mm cutoff. Bivariate and multivariate logistic regression analysis were used to evaluate the association of sociodemographic and clinical factors with false-negative TST results and to develop predictive risk models. Results: TST presented an overall sensitivity of 63.8% (5 mm) and 56.1% (10 mm). HIV infection was the risk factor with the strongest association with false-negative results (aOR 4.65-5 mm; aOR 5.05-10 mm). Other factors such as chronic renal failure (CRF) (aOR 1.55-5 mm; aOR 1.73-10 mm), alcohol abuse (aOR 1.52-5 mm; aOR 1.31-10 mm), drug abuse (aOR 1.90-5 mm; aOR 1.76-10 mm) or age ≥65 years (OR 1.69-5 mm and 10 mm) were also associated with a probability of false-negative results. Conclusion: These results highlight the importance of knowing which factors influence TST results, such as HIV status, substance abuse or age, thus improving its usefulness as a screening method for LTBI.