Concordance in temporally distinct blood and sputum inflammatory phenotypic measures in severe asthma

<b>Rationale:</b> Severe asthma is a heterogeneous disease with different inflammatory phenotypes based on blood or sputum measures. Increasingly blood eosinophils (Eos) are used to direct therapy choice but there is limited information how stable inflammatory measures in sputum and blood are over time and how they relate. <b>Method:</b> Sputum was successfully induced in 48 severe asthma patients at 2 timepoints within 2 years. At each timepoint a full blood count was completed. Patients were at least 4-weeks clear of exacerbation and considered stable. The percentage of granulocytes were reported and the stability at these two timepoints was assessed using Spearman’s rho. <b>Results:</b> In this cohort the sputum Eos and blood Eos significantly correlated between the two timepoints (sputum r=0.739,p=&lt;0.005, blood r=0.387,p=0.011). There was also a significant correlation between the Eos proportions in the two compartments (mean blood vs mean sputum Eos r=0.563,p=&lt;0.005). In contrast, although blood neutrophils (Neut) significantly correlated between the two timepoints (r=0.664,p=&lt;0.005), there was no significant correlation between sputum Neut (r=0.125,p=0.397). Circulating Neut did not reflect sputum Neut (r=-0.083,p=0.602). No correlation was seen with granulocyte measurements, lung function, asthma control or disease duration. <b>Discussion:</b> These results demonstrate that airway neutrophilic inflammation is more dynamic than eosinophilic inflammation and poorly reflected in peripheral blood. A greater understanding of the underlying factors responsible for airway neutrophilic changes is needed if progress is to be made in addressing this severe asthma phenotype.