Substantial differences in severe asthma prevalence and disease characteristics have been reported worldwide, which suggests that ethnicity may have an important role in the etiology and severity of the disease. In a recent international comparison, disparities were evident in lung function, blood eosinophil counts, comorbidities, and medication use across the United States, Europe, South Korea, and Australasia. In the United Kingdom, South Asian and Black patients with asthma are at increased risk for hospital admission compared with White patients, and large ethnic disparities have been reported in rates of hospital readmission. Evidence from the United States similarly suggests higher mortality and rates of asthma exacerbation and hospitalizations among Black people. However, there is limited evidence exploring differences by ethnicity in those with severe asthma, even though these patients experience poor health care–related quality of life and drive much of the health care cost of asthma. Several mechanisms could explain the differences in asthma presentation. Evidence of ethnic differences in the biological predictors in severe asthma from the United States and an association between exacerbation frequency and African genetic ancestry support a genetic contribution. However, disentangling genetic effects from environmental factors among often more disadvantaged Black and underrepresented ethnic populations remains difficult, and other researchers reported that substantial racial disparities in health care use rates are largely or completely mediated by socioeconomic and environmental exposure variables such as income and housing conditions. Cultural differences and disparities in asthma medication adherence and health literacy have also been identified. Differences globally in environment, resources, and health care system organization may also underpin disparities and can confound intercountry comparisons. Leveraging the multiethnic makeup of the UK population facilitates comparison within one country, which is less affected by largely unmodifiable health care organizational and environmental factors.

In this study, we report differences in severe asthma presentation and treatment by ethnicity across two independent cohorts spanning UK primary and specialist care. By analyzing phenotypic characteristics and health care use, we specifically aim to address possible mechanisms underlying these differences, which is necessary to design interventions to narrow disparities and improve care for all patients. In particular, we investigate disparities in type 2 biomarkers that previously were prospectively linked with severe asthma outcomes. Severe asthma patients from underrepresented ethnic groups presented with a higher disease burden and were more likely to attend the emergency department. They had a distinct phenotypic presentation and differences in medicine use, with higher levels of type 2 biomarkers.