Sputum eosinophils may help guide asthma control
medwireNews: Individual fluctuations in eosinophilic inflammation are associated with asthma control, show data from patients in daily practice.
“This study encourages the clinician to monitor eosinophilic inflammation to reduce it as much as possible,” say Sophie Demarche (University of Liege, Belgium) and co-authors.
Their longitudinal trial involved 187 patients with asthma who had at least two successful sputum inductions over a median follow-up period of 1.2 years.
In multivariate analysis, within-subject variations in sputum eosinophils were found to be significantly associated with Asthma Control Questionnaire (ACQ)-6 score (p<0.001) after taking into account variations in forced expiratory volume in 1 second (FEV1), the ratio of FEV1 to forced vital capacity, and inhaled and oral corticosteroid dose.
The researchers note that variations in inhaled corticosteroid (ICS) dose were not independently associated with asthma control, however.
“This suggests that the way through which ICSs bring asthma control is by modulating eosinophilic inflammation,” they write in The Journal of Allergy and Clinical Immunology: In Practice.
The team created receiver-operating characteristic curves to determine the threshold at which eosinophilic inflammation corresponded to an improvement in asthma control, based on a minimal important difference in the ACQ score between the first and last visit of at least –0.5 points.
For the 137 patients of the initial cohort with intermittent or persistent eosinophilic asthma, based on a sputum eosinophil count of 3% or more at any visit, an absolute decrease of 4.3% in sputum eosinophils (area under the ROC curve [AUC], 0.69; p<0.001), or a 3.4-fold reduction (AUC, 0.65; p=0.003), was the minimum needed for a significant improvement in asthma control.
By contrast, a significant worsening of asthma control was associated with a 3.5%, or 1.8-fold, increase in sputum eosinophils (AUC, 0.67; p=0.004 and AUC, 0.63; p=0.02, respectively).
Based on a decrease of 4% or more, the researchers report that sputum eosinophils distinguished patients with improved asthma control from those with no change with 68% sensitivity, 64% specificity, and positive and negative predictive values of 57% and 74%, respectively. Similarly, an increase of 4% or more distinguished patients with worsening asthma control from those with no change with 50% sensitivity, 80% specificity, and positive and negative predictive values of 42% and 85%, respectively.
The associations between asthma control and sputum eosinophils were confirmed in a validation cohort of 79 patients with asthma, as were the minimal important differences, Demarche and team report.
“Our data suggest that patients with uncontrolled asthma in clinical practice with residual eosinophilic inflammation despite usage of corticosteroids have room for improvement in asthma control by intensifying treatment with ICS,” the researchers conclude.
They add that this is in line with observed benefits to increasing existing ICS doses or initiating anti-interleukin-5 treatment to further decrease eosinophilic inflammation.
“Conversely, in patients with noneosinophilic asthma, it is unlikely that an increase in the ICS dose will improve asthma control,” they note.
By Lucy Piper
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