P196 C-reactive protein in giant cell arteritis

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Abstract Background/Aims Giant cell arteritis (GCA) is the commonest primary systemic vasculitis in people over the age of 50. Traditionally, the erythrocyte sedimentation rate (ESR) has been used for clinical assessment of individuals with suspected GCA. The C-reactive protein (CRP) is a cheap, rapid blood test which is replacing ESR. Prior work from a cohort of 119 patients with GCA have shown 3/119 patients to have a normal CRP (0-5 mg/L). Another study has shown a CRP of 26.9 mg/L as the optimal cut-off as a diagnostic test. We analysed the pre-treatment CRP levels to a) determine the proportion of patients with GCA with a normal CRP, b) analyse whether CRP can serve as a discriminant test for diagnosis of GCA, and if so, what the optimal cut-off might be. Methods We analysed the CRP levels of 1000 consecutive patients referred to our GCA service. A diagnosis of GCA was established by either ultrasonography, biopsy or PET scan. The data were analysed using SPSS v28. A comparison of CRP between those with and without GCA was done using Mann-Whitney U test. A ROC curve was used to assess discrimination of CRP for GCA. Results 982/1000 individuals had a pre-treatment CRP level. 304 had GCA. The median (interquartile range) CRP for those with GCA was 61 (78), and those without GCA was 9 (36) (p < 0.0001 using Mann-Whitney U test. The ROC curve had an area under curve of 0.787 (95% confidence interval 0.758, 0.816) (Figure 1). A CRP of >/= 20.5 had 84.2% sensitivity and 63.9% specificity. 13/304 patients with GCA (4.2%) had a normal CRP (</=5 mg/L). Conclusion In a large cohort of consecutive patients with GCA, a CRP threshold of 20.5 can serve as a discriminant test in patients with a clinical suspicion for GCA. 4.2% of patients with GCA may have a normal pre-treatment CRP. Disclosure G. Ducker: None. F.L. Coath: None. S. Fordham: None. C.B. Mukhtyar: None.