Influence of Cigarette Smoke on Results of Hematological and Immunological Investigations in Patients Exposed to Mycobacterium tuberculosis

to the editor—In their report on association of contact characteristics, exposure, and disease phenotype of household contacts with positive interferon-γ release assay (IGRA) from the INFECT case contact cohort study in Indonesia, the authors found that the hemoglobin concentration was significantly lower in people who remained IGRA negative after exposure to a contact with tuberculosis compared to those who converted from negative to IGRA positive. Risk of IGRA conversion was positively associated with hemoglobin concentration [1]. An accompanying editorial incorrectly stated that the risk of incident infection but not prior infection was inversely associated with hemoglobin concentration [2]. A detailed look at smoking history may provide an explanation for the hematological changes observed: Smoking is associated with increased hemoglobin concentrations [3]: Both in baseline IGRA-negative and IGRA persistently negative participants, there was a higher percentage of people who never smoked (69.5% vs 65.0%...