D2.521 - Reshaping Allergy Assessment Pathways In The United Kingdom: Modeling System-Level Gains Through Discrete Event Simulation

Allergy assessment in the United Kingdom remains concentrated in specialist settings despite substantial primary-care burden and long waiting times, creating  inefficiencies that at the end impact patient management and quality of life. Nine National Health Service (NHS) pilot pathways (programs testing new ways to deliver care) introduced a systematized early-assessment approach using structured symptom evaluation and pre-referral serologic specific IgE testing within updated referral guidelines. This modeling exercise used discrete event simulation (DES) to evaluate the system-level impact of scaling these pathways.

 A DES model was developed using epidemiologic and care-pathway parameters from recent Clinical Practice Research Datalink (UK government-supported research data resource) analyses, supplemented by additional literature on allergy presentation rates, referral behavior, prescribing patterns, and coincident asthma incidence and timing. Usual-care trajectories were modeled from first presentation through pathway completion. Redesigned pathway parameters reflected NHS pilot specifications, including early testing, structured triage, and modified referral rules. Outcomes included referral appropriateness, avoidable specialist activity, diagnostic-phase costs, asthma-related events, and system-level indicators such as waiting-list duration, throughput, and flow stability. Scenario analyses varied gatekeeping strength, uptake rates, and key demand parameters to assess uncertainty.

The redesigned pre-referral pathways improved early differentiation of allergic versus non-allergic disease, with higher identification accuracy in all scenarios. In conservative scenarios, referrals declined by about 25 %, and under stronger gatekeeping and higher primary-care retention, reductions approached 60 %. Simulation results indicated improved system flow, with conservative scenarios reducing specialist waiting lists by approximately four months. Diagnostic cost per referred patient remained stable because testing shifted earlier in the pathway rather than increasing overall volume. System performance improved through reduced queue abandonment, lower avoidable specialist activity, and more efficient referral flow and throughput across scenarios.

This modeling exercice suggests that systematized primary-care allergy assessment can reshape patient flow, reduce pressure on specialist services, and improve pathway throughput in ways aligned with health technology assesment role as a system shaper. Discrete event simulation indicates that scaling these NHS pilots could generate broader system benefits. Prospective evaluation will clarify long-term clinical and operational effects.