Background The UK Severe Asthma Registry (UKSAR) collects standardised data on patients referred to specialist difficult asthma services in England, Scotland and Northern Ireland since 2015. It aims to characterise the patient population, standardise high-quality care, and facilitate research into the assessment and clinical management of severe asthma.

Methods Individual patient data from the UKSAR were analysed. Data were presented as mean (standard deviation [SD]) or median (inter-quartile range [IQR]) as appropriate.

Results Data from 2,397 patients were analysed from 20 centres. The mean age was 47.3 (15.5), and most were female (65.5%). The vast majority of patients were Caucasian (78.5%), while almost half were obese (BMI>30, 49%). Patients were generally never- (71%) or ex- (26.1%) smokers, atopic (65.5%), with frequent rescue steroid use in previous year (4+, 60.0%). The mean age of onset was 23 years (19). Mean FEV₁ was 69.1% (23.1) with 22% having significantly impaired lung function (FEV₁ <50%). 59.7% of patients had a FEV₁/FVC ratio <70% suggesting some fixed airflow obstruction. Median blood eosinophils, FeNO and IgE were 0.30 cells/uL (0.13, 0.59), 36.0 ppb (18.0, 72.0) and 161 (49, 485) respectively. Mean ACQ-7 scores were 3.1 (1.3), with the majority of patients uncontrolled (ACQ-7>1.5, 86.7%). 89.2% of patients were taking high dose (>1000mcg BDP equivalent) ICS. 85.2% were receiving a LABA, mostly with formoterol-containing preparations. Over half (52.2%) were taking a LAMA with the majority of these tiotropium (94.0%). 51.4% of patients used LTRAs while 7.2% used macrolide antibiotics. Nearly half (48.3%) of patients were treated with maintenance OCS. A significant minority of patients (19.7%) were thought to be poorly adherent with maintenance medications. Following multidisciplinary review, 90.6% met ATS/ERS criteria for severe asthma and 52.6% of patients progressed to biologic therapy, most commonly with Mepolizumab (68.6%), Omalizumab (24.2%) and Beralizumab (6.9%).

Conclusions Patients referred to UK specialist difficult asthma services have substantial unmet need due to significant asthma symptoms, impaired lung function and high exacerbation rates. Evidence of elevated Type-2 biology is frequently present. Add-on treatments are common at registration, particularly OCS, LAMAs and LTRAs. Over half progressed to biologic therapy.