Objectives To evaluate the effectiveness of using electronic registers to identify and improve management of high-risk asthma patients in primary care.

Design Cluster-randomised controlled trial with stratification by high/low deprivation scores and 1-year follow-up.

Participants 29 GP practices in Norfolk, UK with suitable software systems used electronic searches and clinical knowledge to identify 911 patients aged 5+ years at high risk from their asthma as defined by British asthma guidelines (severe asthma plus adverse psychosocial characteristics, including poor adherence).

Intervention Intervention practices established registers of high-risk asthma patients and used an electronic alert to identify these patients at all practice encounters. This allowed reception staff to prioritise appointments and facilitate patient access to clinicians and clinical staff to review patients' asthma at all opportunities. Practice staff received a 1-h tailored training session on the use of alerts and actions to be taken from a GP (MN) and nurse (JW). Control practices continued with routine care.

Outcomes A composite measure of moderate–severe exacerbations (primary outcome, see Abstract S137 Table 1 for definition), disaggregated exacerbation-related events, consultations and medications (secondary outcomes) were derived from anonymous clinical data extracted from practice-based patient records for the year before and after implementation of registers.

Results See Abstract S137 Table 1 for results of unadjusted analyses. After adjustment for relevant covariates at baseline similar effects were observed but only the effect on nebulised β-agonists prescriptions remained significant.

Conclusions Use of at-risk registers had no significant effect on the overall rate of moderate–severe exacerbations. However, they were associated with increases in prescriptions of oral steroids, inhaled steroids and long-acting β-agonists, coupled with reductions in asthma hospitalisations, prescriptions of nebulised short-acting β-agonists and in failures to attend primary care appointments. Together these are suggestive of improved asthma management in the intervention group.