Diagnostic use of ultrasound in giant cell arteritis in Counties Manukau District Health Board, New Zealand

Objectives A retrospective observational study was undertaken to assess the diagnostic performance (sensitivity and specificity) of colour duplex ultrasound (CDUS) compared with temporal artery biopsy (TAB) for the diagnosis of GCA in the Counties Manukau District Health Board (CMDHB), New Zealand using clinical diagnosis as the reference standard. Methods The study population included patients with clinically suspected GCA who were referred to Middlemore Hospital and underwent CDUS, TAB or both between January 2019 and December 2020. Results Sixty-nine patients were included in the study. Sixty-one percent were >75 years of age, with no cases <50 years of age and a female predominance of 71%. The sensitivity of CDUS was 26% (95% CI 10, 48) and specificity was 97% (95% CI 84, 100). The sensitivity of TAB was 57% (95% CI 34, 77) and specificity was 100%. CDUS had a positive predictive value of 86% (95% CI 42, 99) and a negative predictive value of 65% (95% CI 49, 78). Conclusion A positive CDUS in patients with a high risk for GCA may preclude the need for TAB due to the high specificity of CDUS in GCA. In contrast, patients with a high risk for GCA with a negative CDUS may still need TAB to confirm or exclude GCA. The duration from commencement of steroids to the time of CDUS is crucial in confirming GCA and, for this, shortening the waiting time in the CMDHB would be necessary to ensure adequate test performance in practice.