Full blood count as an ancillary test to support the diagnosis of giant cell arteritis

Temporal artery biopsy is considered the investigation of choice to diagnose definitively giant cell arteritis (GCA) in patients with compatible symptoms. However it is invasive and not completely sensitive. Serum markers, particularly erythrocyte sedimentation rate (ESR), can be supportive, but are not definitive in individual cases.

To investigate whether indices derived from the full blood count, including neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) were associated with a positive biopsy in patients with suspected GCA.

The clinical and pathological details of 537 patients undergoing temporal artery biopsy at our institution from 1992 to 2015 were reviewed.

In univariate analysis high platelets (odds ratio (OR) 4.44, P < 0.001), NLR (OR 1.81, P = 0.02), PLR (OR 3.25, P < 0.001), C-reactive protein (CRP) (OR 3.00, P < 0.001), ESR (OR 3.62, P < 0.001) and increased age (OR 1.03, P = 0.006) were strongly associated with a positive biopsy. In multivariate modelling only high platelets (P < 0.001) and ESR (P = 0.049) maintained significance.

We conclude that the presence of thrombocytosis and high NLR, PLR, ESR and CRP can all be used clinically to support the diagnosis of GCA prior to biopsy. Of particular note, in multivariate modelling the presence of thrombocytosis is a stronger predictor of a positive temporal artery biopsy than ESR. Therefore, careful consideration of the findings in a full blood count can be used to predict the likelihood of a positive temporal artery biopsy in patients with suspected GCA.