CRP and polyarteritis nodosa: Determining levels of disease activity in PAN and TAK patients has proved challenging for several reasons: vascular imaging of medium- or large-sized vessels is frequently invasive and may not reliably differentiate between active inflammation versus damage; biopsy of affected vessels is often too risky and not feasible on a repeated basis; and traditional markers of inflammation (C-reactive protein and erythrocyte sedimentation rate) are non-specific and may not be elevated in organ-limited disease.