Clinical implications of initial peripheral eosinophilia in acute eosinophilic pneumonia

Background and objective The initial peripheral eosinophil count ( PEC ) is rarely elevated but tends to increase during the clinical course of acute eosinophilic pneumonia ( AEP ). We evaluated whether initial peripheral eosinophilia is an indicator of mild disease in patients with AEP . Methods We retrospectively examined associations between initial peripheral absolute eosinophil count, inflammatory markers and clinical characteristics in 85 patients with AEP . Results Of 85 patients, 24 (28%) had initial peripheral eosinophilia (>500/μL). Initial peripheral absolute eosinophil count was inversely correlated to white blood cell ( WBC ) count (ρ = −0.386, P  < 0.001), neutrophil percentage (ρ = −0.645, P  < 0.001) and C ‐reactive protein ( CRP ; ρ = −0.495, P  < 0.001). During treatment, peripheral absolute eosinophil counts increased, while inflammatory markers ( WBC , neutrophil percentage, and CRP ) decreased. Patients with initial peripheral eosinophilia had a longer duration from onset of symptoms to admission ( P  = 0.006), had lower WBC counts, neutrophil percentages and CRP values (all P  < 0.001), and higher oxygen saturation ( P  = 0.004) than patients with normal peripheral eosinophil counts. Oxygen requirements ( P  = 0.013), duration of oxygen administration ( P  = 0.028) and intensive care unit admission rates ( P  = 0.003) were lower in patients with initial peripheral eosinophilia. All patients survived and recovered fully after corticosteroid or conservative treatment. Conclusions Initial PEC may be related to a milder disease status on admission, compared with normal PEC in patients with AEP . This may help to stratify disease severity in AEP .