Systemic Immune-Inflammation Index is associated with flare-related and intercritical inflammatory activity in gout: a longitudinal real-world repeated-measures study.

Gout is traditionally monitored through serum urate levels (SUA). However, the inflammatory component of the disease may not fully parallel short-term urate fluctuations. We aimed to evaluate longitudinal within-patient dynamics of systemic inflammatory activation and to determine whether inflammation persists beyond clinically apparent flares and may not always reflect contemporaneous SUA. Patients with gout were assessed across three successive outpatient clinic visits. Systemic immune-inflammation index (SII), calculated from the values of the complete blood count, and SUA were measured at each visit. Gout flares, as documented in medical records, were analyzed in relation to inflammatory indices, SUA, and visit order using models adjusted for age and sex. Median SII was significantly higher in patients with gout compared with controls (544.5 vs. 383.9, p < 0.001). Non-flare visits were associated with lower SII values compared with flare visits (β = -203.7, SE = 52.6, p < 0.001), independent of age, sex, visit order, and SUA levels. Notably, visit-specific SUA was not independently associated with SII, and no interaction was observed between flare status and SUA. Elevated inflammatory activity was detectable across visits and was not fully explained by acute flare episodes. Systemic inflammatory activity in gout may persist beyond clinically apparent flares and may not always be fully captured by serum urate levels alone. These findings suggest that inflammatory activity and urate levels do not always align in routine clinical practice, highlighting the potential value of complementary inflammatory assessment.