<h3>Background:</h3> Different clinical (probability score for giant cell arteritis (PSGCA)) (1) and ultrasonographic (US) score (UHS) (2) have been proposed to identify patients with giant cell arteritis (GCA) at disease onset. <h3>Objectives:</h3> We propose a simplified US score to correctly identify GCA patients in the setting of GCA fast track clinic. <h3>Methods:</h3> All patients with suspected GCA seen at our rheumatological centre are evaluated according to a clinical, laboratory and US protocol before execution of superficial temporal artery biopsy (TAB). Bilateral US examination of all the temporal branches were done with an Esaote MyLabClassC machine equipped with a 22MHz linear probe. Images of all arterial segments were stored and reviewed for subsequent measurement of right frontal branch intima media thickness (FBIMT) by a rheumatologist blind to the final clinical diagnosis and to the results of TAB histological examination. The validity of the FBIMT was assessed using the area under the curve (AUC) of the receiver operating characteristic curve (ROC) for discrimination and was compared to the AUC of PSGCA and UHS. Sensitivity and specificity were calculated for each sum score of the FBIMT. Correlation coefficients (Spearman rho) was calculated between each score and ESR and CRP values at baseline. <h3>Results:</h3> Table 1 shows comparisons between GCA vs non GCA patients (clinical diagnosis) and GCA biopsy positive vs GCA biopsy negative patients. Correlation coefficients between the different scores were FBIMT/PSGCA 0.479 (p&lt;0.001), FBIMT/UHS 0.806 (p&lt;0.001) and between scores and ESR and CRP levels were FBIMT/ESR 0.306 (p&lt;0.001), FBIMT/CRP 0.394 (p&lt;0.001), PSGCA/ESR 0.443 (p&lt;0.001), PSGCA/CRP 0.468 (p&lt;0.001), UHS/ESR 0.333 (P&lt;0.001) and UHS/CRP 0.389 (P&lt;0.001). FBIMT AUC to discriminate GCA vs non GCA patients (clinical diagnosis) was 0.863 (95%CI=0.803-0.923), similar to PSGCA AUC (0.823;95%CI= 0.752-0.893) or UHS AUC (0.840;95%CI=0.771-0.910). FBIMT AUC to discriminate TAB positive vs TAB negative patients was 0.849 (95%CI=0.791-0.916), without differences with PSGCA AUC (0.791;95%CI= 0.715-0.867) or UHS AUC (0.848;95%CI=0.780-0.916). A right frontal US IMT cut off value of 0.24 had a sensitivity of 0.70 (95%CI 0.59-0.79), a specificity of 0.94 (95%CI 0.83-0.99), a LHR+ of 11.63 (95%CI=3.85-35.14), a LHR- of 0.32 (95%CI=0.23-0.45), a PPV of 0.72 (95%CI 0.74-0.79), a NPV of 0.87 (95%CI 0.76-0.93), and a OR of 36.1 (95%CI 10.3-126.8) for correctly classify GCA at first visit. A right frontal US IMT cut off value of 0.24 had a sensitivity of 0.72 (95%CI 0.61-0.82), a specificity of 0.91 (95%CI 0.79-0.97), a LHR+ of 7.65 (95%CI=3.28-17.81). a LHR- of 0.31 (95%CI=0.21-0.44), a PPV of 0.92 (95%CI 0.83-0.96), a NPV of 0.69 (95%CI 0.60-0.76), and a OR of 24.9 (95%CI 8.8-70.7) for correctly classify TAB positive patients at first visit. <h3>Conclusion:</h3> IMT of the frontal TA branch has high LHR+, sensitivity, specificity, PPV and NPV to correctly classify GCA patients at first visit in a GCA fast track clinic. <h3>REFERENCES:</h3> [1] Laskou F, et al. A probability score to aid the diagnosis of suspected giant cell arteritis. Clin Exp Rheumatol. 2019; Suppl 117(2):104-108. [2] van der Geest KSM, et al. Novel ultrasonographic Halo Score for giant cell arteritis: assessment of diagnostic accuracy and association with ocular ischaemia. Ann Rheum Dis. 2020 Mar;79(3):393-399. <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>

POS1434 ULTRASONOGRAPHIC EVALUATION OF TEMPORAL ARTERY FRONTAL BRANCH AS A DIAGNOSTIC TOOL FOR GIANT CELL ARTERITIS