Development of a Target Product Profile for a Proteomic Blood Test to Aid the Diagnosis of Cranial Giant Cell Arteritis - Study protocol

Background. Giant cell arteritis (GCA) is the commonest systemic vasculitis and a medical emergency. High-dose glucocorticoids are started on suspicion, before confirmation, and cause substantial dose-dependent harm in the many patients who prove not to have GCA. Diagnostic confirmation by temporal artery biopsy or ultrasound remains imperfect. The performance of both approaches is influenced by the clinical context and, for ultrasound, operator expertise, creating the potential for both unnecessary treatment and delayed or missed diagnosis. A laboratory-based, multi-analyte proteomic blood test may help, but its intended use and performance requirements are undefined. Objective. To develop, by structured expert consensus, a Target Product Profile (TPP) for a laboratory-based, multi-analyte proteomic blood test to aid the diagnosis of cranial GCA in secondary care, used alongside clinical assessment, imaging and/or biopsy, with the primary objective of reducing unnecessary glucocorticoid exposure without increasing missed cases, from a UK health-system perspective. Methods and analysis. A multidisciplinary committee of approximately 15 to 30 members, including patient and public representatives, will follow a three-phase process: a scoping phase that confirms the intended use and the prioritised list of characteristics; a drafting phase that specifies minimum (acceptable) and preferred (desirable) values across the TPP domains, using outcome-based methods where feasible; and a consensus-building phase using an up-to-three-round modified Delphi (75% consensus threshold) with interim consensus meetings and a 28-day public consultation. Reporting follows ACCORD and CREDES.