There have been several reports of associations between the FTND score, from which TTFC is derived, and respiratory endpoints. Higher FTND scores, which indicate greater addiction to nicotine and smoking [11], are associated with greater risk of COPD [7, 28], although the association may vary by sex [7]. While one study using computed tomography (CT) imaging found that FTND score was inversely correlated with CT-defined emphysema and COPD severity, the authors conceded that these findings may be largely due to selection bias and other biological processes which may lead to increased lung density in smokers [29]. Smokers with COPD have higher FTND scores, which reflects greater dependency on nicotine, compared to both smokers without COPD [8] and to individuals who quit smoking after COPD diagnosis [28, 30]. Higher FTND scores were also associated with emergency-room admission for smoking-related conditions, compared to admission for other conditions [31], and with more negative symptoms among smokers engaged in cessation efforts [32]. These data, along with our findings, suggest that TTFC is an important predictor of lung disease, but further evaluation is needed. In
