An elevated blood eosinophil count in stable asthma predicts exacerbations and therapeutic response to corticosteroids or biologics targeting eosinophils. However, the prognostic value of blood eosinophils measured at exacerbation remains unknown.

The purpose of a new study published in Clinical and Experimental Allergy was 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.

This was a real-world retrospective review of all life-threatening asthma cases admitted at four public hospitals in Singapore from 2011-2015. Here, trends and correlations between blood eosinophil count on admission, along with arterial blood gas values, duration of mechanical ventilation and risk of death, hypoxic ischemic encephalopathy or respiratory arrest were assessed.

Overall, 376 index life-threatening exacerbations occurred with median blood eosinophil count (5-95th percentiles) of 0.270×109 /L (0-1.410×109 /L). Arterial pH decreased and PCO2 increased with increasing eosinophil count. Meanwhile, the duration of mechanical ventilation and risk of death, hypoxic ischemic encephalopathy or respiratory arrest did not vary with eosinophils. Among 329 survivors who were followed-up over a median of 52 months, blood eosinophils ≥ 1.200×109/L was associated with an increased hazard of emergency visits and/or admissions for asthma.

The findings suggested that in life-threatening asthma, a spot blood eosinophil count correlates to the severity of respiratory failure and predicts the risk of subsequent exacerbations.