Purpose: Exploring whether smoking is an influencing factor for the inconsistency between QuantiFERONTB Gold assay (QFT-GIT) and tuberculosis etiology.
Patients and Methods: The clinical data of patients who were confirmed positive for Mycobacterium tuberculosis (MTB) after undergoing QFT-GIT testing from September 2017 to August 2021 were retrospectively analyzed. Chi-square and rank-sum tests were used to compare the differences in characteristics between smokers and non-smokers. Logistic regression was used to adjust for confounding factors affecting smoking. Propensity score matching (PSM) was used to verify the above conclusions again.
Results: Positive results of tuberculosis etiology were adopted as the standard, the incidence of inconsistent results between QFT-GIT and tuberculosis etiology was 8.90% (108/1213), of which the false negative rate was 6.27% (76/1213) and the indeterminate rate was 2.64% (32/1213). In the overall population, the smokers had a lower level of basal IFN-γ (Z=− 2.079, P =0.038). Among 382 elderly (≥ 65 years old) patients, the smokers had lower levels of antigen-stimulated IFN-γ (Z=− 2.838, P =0.005). After performing BOX-COX transformation on all non-normally distributed data, logistic stepwise regression was used to adjust confounding factors. The results showed that smoking was an influencing factor for the inconsistency between QFT-GIT and tuberculosis etiology results (OR=1.69, P =0.020). Using PSM for 1:2 matching, the results showed that smoking was still an independent risk factor for the inconsistent results of QFT-GIT and tuberculosis etiology (OR= 1.95, P =0.019). Age-stratified analysis showed that smoking was an independent risk factor in discordance between QFT-GIT and tuberculosis etiology in patients aged ≥ 65 years (OR=2.40, P =0.005), but not in patients aged < 65 years (P > 0.05). 
Conclusion: Smoking can reduce the body’s IFN-γ release ability, and smoking (especially the elderly) is an influencing factor for the inconsistency between QFT-GIT and tuberculosis etiological results.
Keywords: tuberculosis etiology, PSM, inconsistency, influencing factors