Stability in eosinophil categorisation during subsequent severe exacerbations of COPD

Abstract

Background: The blood eosinophil count has been shown to be a promising biomarker for establishing personalised treatment strategies to reduce corticosteroid use, either inhaled or systemic, in chronic obstructive pulmonary disease (COPD). Eosinophil levels seem relatively stable over time in stable state, but little is known whether this is also true in subsequent severe acute exacerbations of COPD (AECOPD).

Aims and objectives: To determine the stability in eosinophil categorisation between two subsequent severe AECOPDs employing frequently used cut-off levels.

Methods: During two subsequent severe AECOPDs, blood eosinophil counts were determined at admission to the hospital in 237 patients in the Cohort of Mortality and Inflammation in COPD Study. The following four cut-off levels were analysed: absolute counts of eosinophils ≥0.2×10⁹/L (200 cells/µL) and ≥0.3×10⁹/L (300 cells/µL) and relative eosinophil percentage of ≥2% and ≥3% of total leucocyte count. Categorisations were considered stable if during the second AECOPD their blood eosinophil status led to the same classification: eosinophilic or not.

Results: Depending on the used cut-off, the overall stability in eosinophil categorisation varied between 70% and 85% during two subsequent AECOPDs. From patients who were eosinophilic at the first AECOPD, 34%-45% remained eosinophilic at the subsequent AECOPD, while 9%-21% of patients being non-eosinophilic at the first AECOPD became eosinophilic at the subsequent AECOPD.

Conclusions: The eosinophil variability leads to category changes in subsequent AECOPDs, which limits the eosinophil categorisation stability. Therefore, measurement of eosinophils at each new exacerbation seems warranted.

Keywords: COPD epidemiology; COPD exacerbations; eosinophil biology; pulmonary eosinophilia.

Figure 1

Scatter plot for the absolute and relative eosinophil counts measured at both severe AECOPDs. The size of the circle corresponds to the number of measurements with the smallest circle representing one measurement and the largest 66. Left: absolute count. Right: relative count. AECOPD, acute exacerbations of chronic obstructive pulmonary disease.

Figure 2

Stability of eosinophil categorisation over the two severe acute exacerbations of chronic obstructive pulmonary diseases (AECOPDs). Data presented separately for the total cohort, patients without steroid use before both AECOPDs (group 1), patients with steroid use before both AECOPDs (group 2) and patients who used steroids either before the first AECOPD or before the second AECOPD (group 3). The bars show the proportions of patients being categorised as eosinophilic or non-eosinophilic for the four used cut-offs at the first and second AECOPDs.