Variability of Blood Eosinophil Count at Stable-State in Predicting Exacerbation Risk of Chronic Obstructive Pulmonary Disease

Wang Chun Kwok,1 Chi Hung Chau,2 Terence Chi Chun Tam,1 Fai Man Lam,1 James Chung Man Ho1 1Department of Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China; 2Tuberculosis and Chest Unit, Grantham Hospital, Hong Kong Special Administrative Region, People’s Republic of ChinaCorrespondence: James Chung Man Ho, Department of Medicine, Queen Mary Hospital, 4/F, Professorial Block, 102 Pokfulam Road, Hong Kong Special Administrative Region, People’s Republic of China, Tel +852 2255 4542, Fax +852 2816-2863, Email jhocm@hku.hkBackground: Chronic obstructive pulmonary disease (COPD) phenotyping using stable-state blood eosinophil level was shown to have prognostic implication in terms of exacerbation risk. However, using a single cut-off of blood eosinophil level to predict clinical outcome has been challenged. There have been suggestions that variability of blood eosinophil count at stable-state could provide additional information on exacerbation risk.Methods: A retrospective cohort study was conducted in a major regional hospital and a tertiary respiratory referral centre in Hong Kong, including 275 Chinese patients with COPD, to investigate the possible role of variability of blood eosinophil count at stable-state to predict COPD exacerbation risk in one year.Results: Higher variability of baseline eosinophil count, which is defined as the difference of the minimal and maximal eosinophil count at stable-state, was associated with increased risk of COPD exacerbation in the follow-up period with adjusted OR (aOR) of 1.001 (95% CI = 1.000– 1.003, p-value = 0.050) for 1 unit (cells/μL) increase in variability of baseline eosinophil count, aOR of 1.72 (95% CI = 1.00– 3.58, p-value = 0.050) for 1 SD increase in variability of baseline eosinophil count and aOR of 1.06 (95% CI = 1.00– 1.13) for 50 cells/μL increase in variability of baseline eosinophil count. The AUC by ROC analysis was 0.862 (95% CI = 0.817– 0.907, p-value < 0.001). The cut-off for variability of baseline eosinophil count identified was 50 cells/μL, with sensitivity of 82.9% and specificity of 79.3%. Similar findings were also shown in the subgroup with stable-state baseline eosinophil count below 300 cells/μL.Conclusion: Variability of baseline eosinophil count at stable-state might predict the exacerbation risk of COPD, exclusively among patients with baseline eosinophil count below 300 cells/μL. The cut-off value for variability was 50 cells/μValidation of the study findings in large scale prospective study would be meaningful.Keywords: COPD, eosinophil, phenotype, COPD exacerbation