Background. Persistent airflow obstruction (PAO) can occur in young individuals (<50 yrs.). However, the phenotypic differences between PAO in young and older (>70 yrs.) subjects in the general population are unclear.

Aims. To compare phenotypic differences of young vs. old PAO in the general population.

Methods. We contrasted young and old subjects with PAO (post-BD FEV1/FVC<0.7) in the LEAD cohort, a single-centered, observational, population-based study in Vienna (Austria; J Epidemiol 2019: 29(8): 315-324).

Results. We identified 181 young subjects with PAO (40.0±7.4 years, FEV1:83.4±10.8 %GLI, pack years (PY): 11.8±15.4 of whom 61% and 39% had <10 and ?10PY, respectively, and 187 older subjects with PAO (74.2±2.7 years, FEV1:82.6±17.9 %GLI, PY: 27.7±39.6) of whom 47% and 53% had <10 or ?10PY, respectively.

Young subjects with PAO were more frequently current smokers (38.1 vs 18.2%; p<0.001), had a higher diffusion capacity (98.0±15.5 vs 88.3±23.3 %GLI; p<0.001), a more prevalent diagnosis of asthma (30.9 vs 15.0%; p<0.001), lower levels of circulating inflammatory markers and less dyspnea than old PAO.

When stratified by their cumulative smoking exposure, we observed that old PAO with ?10PY had significantly reduced FEV1 vs <10PY, and that young and old PAOs with ?10PY had lower DLCO, reduced asthma prevalence, more symptoms and more inflammatory markers than respective <10PY.

Conclusions. In the general population PAO was largely mild but there are significant phenotypic differences between young and old individuals with PAO. A significant fraction of young PAO did not have substantial smoking history. In contrast, young PAO with ?10PY are more similar to old PAO.