Eosinophilia linked to lung function decline irrespective of asthma symptoms
medwireNews: High blood eosinophil counts are associated with airflow obstruction and lung function decline in patients with asthma, but also in people without respiratory symptoms, population-based study findings show.
Participants with average blood eosinophil counts above 0.4 x 109 L between the ages of 21 and 38 years had declines in the ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) and FEV1 that were 1.8% and 3.4% greater, respectively, than those of individuals with lower counts (p=0.001 in both cases).
The declines in these spirometry measures “were of a similar magnitude to the declines observed among those who smoked 10 pack-years or more over the same time,” Robert Hancox (University of Otago, Dunedin, New Zealand) and co-researchers note.
Patients with asthma had higher blood eosinophil counts than individuals without asthma. Among 81 asthma patients who had eosinophil counts measures at all four assessments (ages 21, 26, 32, and 38 years), the average count was 0.25 x 109 L versus 0.17 x 109 L for the 96 individuals without asthma (p<0.001). And 17% of asthma patients had average eosinophil counts above the 0.40 x 109 L cutoff across all four tests versus 6% of those without asthma (p<0.001).
Yet the degree of decline in FEV1/FVC associated with increasing eosinophil count was similar for individuals with and without asthma, at 5.4% and 4.7% per 1 x 109 L, respectively, and significant in both cases (p<0.001 and p=0.028, respectively). The associated decline in FEV1 was also similar between the two groups, at 7.0% per 1 x 109 L for individuals with asthma (p=0.052) and 7.8% per 1 x 109 L for individuals without asthma (p=0.004), with the former association reaching significance after taking into account patients who smoked 10 pack–years or more.
And when comparisons were made between patients with and without wheeze, the findings were largely similar, although associations between eosinophil count and post-bronchodilator measured FEV1/FVC and FEV1 were only significant for patients with wheeze.
The researchers report in the European Respiratory Journal that the associations between eosinophil count and FEV1/FVC and FEV1 were seen both for pre- and post-bronchodilator measurements and were independent of timing of asthma diagnosis (childhood or adulthood), cumulative smoking exposure, and lung function during early adulthood, and unaffected by adjustment for body mass index and atopic sensitization.
“Our findings suggest that long-term eosinophilic airway inflammation may worsen lung function decline and increase the risk for COPD [chronic obstructive pulmonary disease],” note Hancox and colleagues.
“This is important because it may be possible to prevent this with treatment.”
The researchers add: “We need information from prospective randomised controlled trials to establish whether treating eosinophilic inflammation with inhaled corticosteroids would improve long-term outcomes for lung function in either COPD or asthma.”
By Lucy Piper
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