Background/Purpose: Giant Cell Arteritis (GCA) is the most common large vessel vasculitis which can result in irreversible blindness if not diagnosed and treated promptly. We run a consultant led Fast Track GCA clinic (FTC) to ensure a rapid assessment and treatment of patients with GCA.

A GCA pre-test probability score is important to prioritise referrals, ensure patients are triaged safely, prevent unnecessary burden of steroid treatment on patients and reduce service pressures.

The aims of our study are to externally validate the use of the Southend GCA probability score (SGCAPS) in our FTC which covers the Stockport and Cheshire region of Greater Manchester, UK. The SGCAPS was developed in 2019 by Laskou et al and then subsequently shown to successfully risk stratify patients referred to the Southend FTC by Sebastian et al in 2020.

Methods: SGCAPS data was collected prospectively in patients who presented to the Stockport FTC over an 18-month period between April 2020 and September 2021. GCA diagnoses were supported by US of the temporal arteries and axillary arteries with or without temporal artery biopsy and confirmed at 6 months by the responsible clinician. Other additional tests that were used included PET-CT. We applied the SGCAPS score to all patients and risk stratified into three groups: low-probability (LP) (score < 9), intermediate-probability (IP) (score 9-12) and high-probability (HP) (score >12). We assessed the number of GCA cases in each group.

Results: A total of 101 patients were referred to the FTC for suspected GCA during the specified time period. There was a female to male ratio 1.8:1. Mean age 70.6 years old. 33 (32.7%) patients had a confirmed diagnosis of GCA. 58 (57.4%%) patients were divided into the LP group, 31 (30.7%) in the IP group and 12 (%) in the HP group. 1 (1.72%) patient in the LP group, 20 (60.4%) in the IP group and 12 (100%) in the HP group had a diagnosis of GCA. The LP group (GCAPS< 9) had a sensitivity of 96.9% and a specificity of 83.8% for the diagnosis of GCA. The HP group ( >12) had a sensitivity of 36.37% but a specificity of 100% for a diagnosis of GCA. The single patient in the LP group with a diagnosis of GCA had a GCAPS score of 8, as such a score of ≥8 can be used with 100% sensitivity for the diagnosis of GCA (specificity 73.9%). Ultrasound scanning had a sensitivity of 73.4% and a specificity of 96.9% for diagnosis of GCA.

Conclusion: This study supports the use of SGCAPS to risk stratify patients referred to a FTC. The high sensitivity of this test in the LP group means that the SGCAPS can be safely used to rule out GCA at a score < 8. Furthermore, the high specificity of this test in the HP group means that SGCAPS could be used to rule in GCA at score of >12.

Using the SGCAPS < 8 to rule out GCA we could potentially reduce the number of urgent GCA referrals by approximately 50%. Additionally, by not requesting temporal artery ultrasound scans in low-probability patients, we can reduce the number of temporal artery ultrasound scans by 50%. The clinical need for referral and scanning certainly remains important in the intermediate-probability group. Despite the possibility to rule in GCA in patients with a score >12 with 100% specificity, referral and scanning will remain an important part of the best practice management in GCA patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/external-validation-of-a-giant-cell-arteritis-probability-score-gcaps-to-risk-stratify-gca-referrals-experience-from-a-united-kingdom-fast-track-clinic/