Blood eosinophil count correlates with severity of respiratory failure in life-threatening asthma and predicts risk of subsequent exacerbations

Background: An elevated blood eosinophil count when asthma is stable predicts exacerbations and therapeutic response to corticosteroids or biologics targeting eosinophils. Few studies have examined the prognostic value of blood eosinophils measured at exacerbation. Aim: To elucidate the relationship between a spot blood eosinophil count-measured at the onset of a life-threatening asthma exacerbation-with indices of exacerbation severity and risk of subsequent exacerbations. Methods: Real-world, retrospective review of all life-threatening asthma cases admitted at 4 public hospitals in Singapore between 2011-2015. We assessed the trends and correlations between blood eosinophil count on admission with arterial blood gas values, duration of mechanical ventilation, and risk of death, hypoxic ischemic encephalopathy or respiratory arrest. Risk of future exacerbations among survivors was modelled using Cox regression and survival curves. Results: There were 376 index life-threatening exacerbations with median blood eosinophil count (5-95th percentiles) of 0.270 x 10(9)/L (0-1.410 x 10(9)/L). Arterial pH decreased and PCO2 increased with increasing eosinophil count. Duration of mechanical ventilation and risk of death, hypoxic ischaemic encephalopathy or respiratory arrest did not vary with eosinophils. Among 329 survivors who were followed-up over a median of 52 months, blood eosinophils >= 1.200 x 10(9)/L was associated with an increased hazard of emergency visits and/or admissions for asthma (hazard ratio 1.8, 95% confidence interval 1.1-2.9, P =.02). Conclusion: In this study of life-threatening asthma, we found that a spot blood eosinophil count correlates with severity of respiratory failure and predicts risk of subsequent exacerbations.