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

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.