A single blood eosinophil count taken in patients with COPD can predict treatment response to inhaled corticosteroids (ICS) just as accurately as two measurements, UK researchers have shown.

An Oxford University team undertook a post-hoc analysis of data from the randomised InforMing the PAthway of COPD Treatment (IMPACT)  trial to assess whether one or two measurements of the biomarker could better predict the response to ICS treatment.

Their analysis demonstrated “no improvement in prognostic value of a repetition of blood eosinophil count over a short period of time (2 weeks) compared with a single measurement,” which “indicates that a single blood eosinophil count measurement, taken in steady state, could potentially be used to predict a beneficial response to ICS,” the authors wrote in a paper published in the European Respiratory Journal.

The study also found that eosinophil counts remained relatively stable over the assessed timeframe, which “should reassure clinicians that the timing of blood eosinophil count measurement is not critical for accurate prediction of ICS response in a population of patients with COPD, at least over a short time period,” the authors noted.

In the trial, patients with symptomatic COPD remained on their own medication during a two-week run-in period and were then randomised to receive fluticasone furoate/umeclidinium/vilanterol (FF/UMEC/VI), FF/VI or UMEC/VI. Blood eosinophil counts were measured during the run-in period and also at randomisation.

The analysis modelled the treatment effect of FF/UMEC/VI versus UMEC/VI, and FF/VI versus UMEC/VI on exacerbation rates by continuous blood eosinophil count using measurements taken at screening, randomisation, and the mean, minimum and maximum of the screening and randomisation blood eosinophil count values.

The data show a mean and median eosinophil count of 210 cells/μL and 160 cells/μL at screening and 220 cells/μL and 170 cells/μL at randomisation, respectively, giving a median difference of 10 cells/μL between the average measurements. All the models investigated showed that any variation in blood eosinophil count over a 2-week period “had no clinically relevant impact,”  said the authors, led by Professor Mona Bafadhel, a Consultant Respiratory Physician at the Nuffield Department of Medicine.

Several potential limitations of the analysis were highlighted, such as the relatively short time-frame between blood eosinophil measurements and the low number of counts assessed per patient. Also, as participants of the IMPACT trial, patients had relative clinical stability and had been exacerbation-free, and so the cohort may not be representative of a real-world COPD population.

“Nonetheless, the analysis was conducted in a large population (>10,000 patients) allowing assessment of the utility of eosinophil measurements at a population level,” the authors stressed.

GlaxoSmithKline funded the study and editorial support for the research paper.