Blood eosinophil variability has treatment decision effects
medwireNews: Researchers have highlighted the need for blood eosinophils to be repeatedly measured in patients with severe asthma when designating treatment having found that levels vary in individuals over time.
“The development of agents that target IL [interleukin]-5 for treatment of asthma makes it imperative that clinicians have tools to identify patients with eosinophilic characteristics,” say Joan Reibman and colleagues, from New York University School of Medicine in the USA.
The team carried out a retrospective chart review of 219 patients who visited the Bellevue Hospital Asthma Clinic in New York.
Most (74%) of the patients were prescribed combination inhaled corticosteroids and long acting beta agonists, with 23% also prescribed a long acting muscarinic antagonist (LAMA) and 40% prescribed a leukotriene receptor antagonist.
The geometric mean eosinophil count for the patients as a whole was 149 cells/µL, ranging from as low as 10 up to 1156 cells/µL.
Blood eosinophil levels measured over the preceding 5-year period showed that only 6% of patients had levels that were repeatedly above a target threshold of 300 cells/µL, while 46% had levels that never reached 300 cells/µL. The largest group of patients, at 50%, had levels that traversed the 300 cells/µL threshold level.
The researchers were able to identify three clusters of patients. The first, comprising 62 (28%) patients, had little variability in blood eosinophil levels, with a low geometric mean level of 63 cells/µL. The second cluster consisted of 44 (20%) patients who had a large variability in blood eosinophil levels and a slightly higher geometric mean level of 106 cells/µL, while the largest third cluster comprised 113 patients – half of the participants – who had the smallest variability, although they had the highest geometric mean level of blood eosinophils, at 273 cells/µL.
It was the patients with the greatest level of variability in blood eosinophil measures who had the least well-controlled asthma, however.
These patients had been prescribed more controller medications, including LAMAs, than patients in the other two groups, and more of these patients had a history of an asthma hospitalization in the preceding 12 months.
Many patients in this group had a history of intubation, although the difference did not reach statistical significance, and they had the lowest pre- and post-bronchodilator forced expiratory volume in 1 second and forced vital capacity values.
“These findings may be due to differences in intrinsic disease activity as manifest by fluctuating eosinophil levels, or may reflect a response to external stimuli, including that of allergens,” the researchers suggest in Clinical & Experimental Allergy.
The findings raise the question as to whether variability in a patient affects their response to biologic agents that target eosinophils, such as IL-5, they say, explaining that “[a] higher baseline eosinophil count is associated with a clinical response to these agents, however the importance of variability remains to be determined.”
They conclude: “Although patients in Cluster 2, with more blood eosinophil variability, and Cluster 3, with higher blood eosinophil levels but less variability could all be eligible for agents targeting IL-5, it is unclear whether the clinical response to agents that target IL-5 would be similar between patients in these clusters.”
By Lucy Piper
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