Response to Comment on: How common is inflammatory marker-negative disease in giant cell arteritis?

Sir,

We thank Dr Kermani et al¹ for their interest in our article.

In response to their comments on our report² we acknowledge the inadvertent omission of two recent articles,^{3, 4} both of which emphasise the occurrence of CRP-negative disease seen in giant cell arteritis (GCA). Our case is clearly described as ‘CRP-negative disease’, and in addition to this we review inflammatory-marker-negative disease in GCA, as it is appropriate and informative in this context.

The threshold for an abnormal CRP result is ill defined. Indeed various receiver operating characteristic curves for CRP have been published, illustrating the trade-off of sensitivity and specificity at various threshold settings. Also, different laboratories express the parameter as either mg/l or mg/dl, which can be a source of confusion in clinical practice. Hayreh et al⁵ use a level <24.5 mg/l (2.45 mg/dl) as a cut-off for normal in the context of GCA.