Serum Urate as a Surrogate Outcome for Gout Flares: Where Do We Stand Today?

In gout research, serum urate has been widely accepted as the primary endpoint in clinical trials of urate-lowering therapies by both the FDA and EMA for many years. However, for serum urate to be a meaningful outcome measure, it should reflect at least one important patient-centered clinical outcome, such as gout flares. The relationship between achieving a pre-specified “target” serum urate and a corresponding improvement in patient-centered outcomes has been difficult to show due to variation in reporting of both serum urate and gout flares in clinical trials; a paradoxical rise in gout flares after starting urate-lowering therapy and a delay after achieving the pre-specified target serum urate before gout flares settle coupled with the relatively short duration of the trials. However, recent evidence from individual-level patient data from two, two-year randomized controlled trials clearly shows that achieving target urate is associated with a subsequent reduction and cessation of gout flares. In this review, we examine the evidence supporting serum urate as a surrogate outcome for gout flares, the methods, and the challenges of showing the validity of surrogacy.