GOLD committee explains the rationale behind blood eosinophil recommendations

The use of blood eosinophil levels in COPD is moving from a way to simply identify patients who would benefit from inhaled corticosteroids to a broader role as a biomarker, the GOLD committee explains in a review of its guidelines.

Since blood eosinophil count was first included in the 2019 GOLD guidelines as a biomarker, more evidence has come to light about the association with T2 inflammation and the lung microbiome, the committee said.

Writing in the American Journal of Respiratory and Critical Care Medicine, they noted research has provided new insights into the predictive value of blood eosinophils in COPD, which they wanted to set out in more detail than the guidelines allow.

This includes support for thresholds for blood eosinophils of less than 100 cells/ml suggesting little or no benefit of ICS and >300 cells/ml being most likely to benefit but with an awareness it should not be used as a standalone marker of future risk and is only useful in the context of exacerbation history, they said.

They also recommended these are not strict thresholds and small within or between-day variations should not lead to decisions to change clinical management.

In younger people without COPD, there is evidence of an association between higher blood eosinophil count, and both faster FEV1 decline and the development of airflow obstruction, they added.

When it comes to the microbiome, research has shown lower blood eosinophil counts are associated with a greater presence of proteobacteria, notably Haemophilus, and increased bacterial infections and pneumonia – a risk thats seem to be increased by ICS use.

Overall, the findings provide additional reasons not to use ICS in patients with COPD with lower blood eosinophil counts, they added.

“This evidence supports an integrated evaluation of clinical history (notably exacerbation history), [blood eosinophil count], and sputum microbiology to provide a personalised management approach with regard to when ICS should be used on top of LABD and the management of airway infection,” they said.

“The GOLD 2019 report first introduced [blood eosinophil count] as a biomarker to help make pharmacological treatment decisions concerning ICS use in patients with COPD with a history of exacerbations.

“The GOLD 2022 report now adds various additional evidence concerning blood eosinophil count, including the connections [with] T2 inflammation, and lung microbiome, which identify COPD subgroups with increased ICS response (higher blood eosinophil count) or increased risk of bacterial infection (lower blood eosinophil count).”

“These findings further our understanding of COPD subtypes, facilitating precision medicine strategies on the basis of clinical phenotyping combined with endotyping,” the committee concluded.

Professor John Hurst, professor of respiratory medicine at UCL said: “In general, a personalised approach in COPD is always important, and blood eosinophils are one variable I would consider when deciding whether to recommend ICS or not to someone living with COPD.”

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