Lawrence Oh1, Eugene Wong1, Anthony Gill1, Peter McCluskey1,2, James Smith1,2

Purpose: To utilise the American College of Rheumatologist’s diagnostic criteria for giant cell arteritis (GCA) to determine the need for a temporal artery biopsy (TAB) and identify whether length was a significant predictive factor.

Methods: Retrospective case-control study of a consecutive cohort of 545 patients who had undergone TABs across 6 tertiary hospitals between January 1^st 1992 and January 1^st 2016. In patients with either positive or negative TABs, we also collected age, sex, laterality of biopsies, length of biopsy, and erythrocyte sedimentation (ESR). We excluded 7 patients from this cohort as their age at biopsy was less than 50 years.

Results: There were 538 patients in the GCA cohort. ESR ? 50mm/h was a very strong predictor for a positive TAB result (p<0.0001), however the other covariates, excluding length, did not demonstrate a statistically significant association. 23.4% of TABs were positive, with the average length being 17.6mm. There was a significant difference in means for positive (19.9mm) and negative biopsies (16.8mm) (p=0.0009). Each millimetre increase in TAB length increased the odds of a positive TAB by 3.4% (p=0.024). A cut-off point of ? 15mm increased the odds of a positive TAB by 2.25 compared with a TAB less than 15mm (p=0.003).

Conclusion: Clinical manifestation, age and elevated ESR should guide the application of a TAB. ESR ? 50 and length were significant predictors of GCA. The TAB should be a minimum length of 15 mm in order to avoid a false-negative GCA diagnosis, which can have devastating consequences.