The systemic vasculitides are a group of inflammatory disorders charac
terised by relapses and remission. Before the introduction of immunosu
ppressive drugs, mortality was unacceptably high. Immunosuppressive th
erapy has had a therapeutic impact, but at the cost of increased risk
of infection and other adverse effects. Differentiating infection from
active disease can be difficult, and the inappropriate prescription o
f immunosuppressive drugs can be fatal. Hence disease indices which ca
n aid physicians to identify the active phase of disease and enable ea
rly treatment, will be valuable in the management of this group of dis
orders.