Transient Ischaemic Attack (TIA) is a neurologic event with symptom resolution within 24 hours. Early specialist assessment of TIA reduces risk of stroke and death. National United Kingdom (UK) guidelines recommend patients with TIA are seen in specialist clinics within 24 hours (high risk) or seven days (low risk).

We aimed to develop a complex intervention for patients with low risk TIA presenting to the emergency ambulance service. The intervention is being tested in the TIER feasibility trial, in line with Medical Research Council (MRC) guidance on staged development and evaluation of complex interventions.

We conducted three interrelated activities to produce the TIER intervention:

• •Survey of UK Ambulance Services (n = 13) to gather information about TIA pathways already in use
• •Scoping review of literature describing prehospital care of patients with TIA
• •Synthesis of data and definition of intervention by specialist panel of: paramedics; Emergency Department (ED) and stroke consultants; service users; ambulance service managers.

The panel used results to define the TIER intervention, to include:

1. 1.Protocol for paramedics to assess patients presenting with TIA and identify and refer low risk patients for prompt (< 7day) specialist review at TIA clinic
2. 2.Patient Group Directive and information pack to allow paramedic administration of aspirin to patients left at home with referral to TIA clinic
3. 3.Referral process via ambulance control room
4. 4.Training package for paramedics
5. 5.Agreement with TIA clinic service provider including rapid review of referred patients

We followed MRC guidance to develop a clinical intervention for assessment and referral of low risk TIA patients attended by emergency ambulance paramedic. We are testing feasibility of implementing and evaluating this intervention in the TIER feasibility trial which may lead to fully powered multicentre randomized controlled trial (RCT) if predefined progression criteria are met.