P206 Rethinking old biomarkers: novel predictors of giant cell arteritis
Authors: Somoskeoy Tamas , Bourn Alexandra , Knights Sally , Mulhearn Ben 
Published: April 2021

Abstract
Background/Aims
Giant cell arteritis (GCA) is a large vessel vasculitis mainly affecting the arteries of the head and neck which, if untreated, may lead to permanent vision loss. Glucocorticoids are highly effective at turning off inflammation but come with toxic side effects, making prompt diagnosis essential. There is no gold-standard investigation for GCA. Although specific, temporal artery biopsy (TAB) is only positive in approximately 25% of cases making it problematic as a rule-in diagnostic test. Vascular ultrasound may aid diagnosis but there is a rapid reduction in sensitivity with glucocorticoid use and it is not yet universally available. Diagnosis therefore requires the integration of clinical judgment with blood tests measuring inflammation, imaging, and biopsy. Aims:Identify which components of the history, examination and laboratory findings are most predictive of a positive diagnosis of GCA in the local region of Yeovil District Hospital, and to investigate the usefulness of alternative blood biomarkers.
Methods
Data was collected from GCA clinic attendances between August 2018 and February 2020 using electronic notes, clinic letters and the pathology system. Predictive values, sensitivity, specificity, and receiver operating characteristic (ROC) curves were calculated for each individual parameter and for groups of parameters.
Results
Ninety-one patients presented to GCA clinic in the 18 months studied. Median age was 71 and 73% were female. 56 patients with suspected disease went on to have TAB, of which 38/56 (68%) were of adequate length ( &gt; =10mm), and of those, 12/38 (32%) confirmed a diagnosis of GCA. 43/91 (47%) patients were ultimately diagnosed biopsy proven or suspected GCA. Headache was the most common presenting feature (88%) followed by raised ESR (55%), raised CRP (53%), visual disturbance (44%), scalp tenderness (33%), jaw claudication (31%), PMR symptoms (27%) and temporal artery abnormalities (20%). Headache and raised CRP+/-ESR were the most sensitive markers (91% and 100%, respectively). They were, however, the least specific (4% and 36%). Temporal artery abnormality was the most specific finding (81%). ROC analysis revealed that the best-performing biomarkers were monocytes (area under the ROC curve (AUC) of 0.81) and platelets (AUC 0.80), which were superior to jaw claudication, the best-performing classical biomarker (AUC 0.68). Platelets above 450 x 109/L had a specificity of 96% with a likelihood ratio of 10.9. Monocytes above 0.45 x 106/L had sensitivity and specificity of 100% and 67%, respectively.
Conclusion
GCA cannot be accurately predicted by any single feature. In this cohort, absence of headache with a normal CRP+/-ESR ruled out GCA. Platelets and monocytes performed better than all the classical parameters associated with GCA. Validation of these biomarkers in a larger cohort is now needed to ascertain cut-off points which may help to develop a more accurate method to predict cases of GCA.
Disclosure
T. Somoskeoy: None. A. Bourn: None. S. Knights: None. B. Mulhearn: None.