Background/Purpose: The initial suspicion of Giant cell arteritis (GCA) is often made in the setting of primary care or casualty by a non-rheumatologist. Whilst temporal artery biopsy (TAB) is the gold standard for diagnosis, this is not readily available and can be difficult to organise outside a teaching hospital setting. Furthermore, the reliability of this test is reduced by concomitant steroid use and the presence of skip lesions in vessel wall inflammation. Clinical features combined with biochemical markers of inflammation are often the most important tools in the diagnosis of giant cell arteritis. In this study, we evaluate the association of CRP, ESR, platelet count and alkaline phosphatase (ALP) with the results of temporal artery biopsy in a regional setting involving three District General Hospitals in the UK. As it has been over 5 years since the British Society for Rheumatology guidelines were published, we also audited whether our local practice follows them. Particularly, with regard to biopsy length which has been shown to influence the sensitivity of the test.

Methods: A retrospective analysis of all patients referred with suspected temporal arteritis to three centres in South East England between Feb 2010 and May 2015 was performed. Data regarding age, sex, date of biopsy, length of biopsy, biopsy result and ESR, CRP, platelet count and Alkaline Phosphatase (ALP) within 14 days prior to biopsy was collected. 

Results: 542 patients were referred with suspected giant cell arteritis between Feb 2010 and May 2015. 119 patients were excluded owing to inconclusive biopsy findings and lack of laboratory results within 14 days prior to TAB. The majority of excluded patients had blood tests performed at other sites. 422 patients (131 men 291 women) were included. Mean age was 72.4. 95 TABS were positive and 327 negative.  Mean biopsy length was 13.9mm. 32.2% of biopsies were less than 10mm. The mean ESR for positive biopsies was 58.6 versus 40.1 in negative biopsies (p < 0.001 ). 84.3% of patients with a positive temporal artery biopsy were associated with an ESR >10. The mean CRP in those with positive biopsies was 91.1 compared with 50.3 in those with a negative TAB (p < 0.001). 95.8% of patients with a positive TAB had a CRP >10. Patients with positive TABS also had higher platelet counts: mean platelet count was 424 in positive biopsies versus 334 in negative biopsies (p < 0.001). There was no statistical difference in ALP between those with positive and negative biopsies.

Conclusion: Laboratory correlates of inflammation remain good predictors of a positive temporal artery biopsy. A positive biopsy is associated with increased CRP, ESR and platelets. Our study shows that improvements need to be made locally to ensure the recommended temporal artery biopsy length (>10mm) is taken.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/laboratory-tests-in-giant-cell-arteritis-do-they-make-the-cut/