Relationship between serum urate and changes in dual-energy CT monosodium urate crystal volume over 1 year in people with gout: an individual participant data analysis.

Objectives: The dynamics of monosodium urate (MSU) crystal changes across a range of serum urate concentrations in people with gout are unknown. This study aimed to systematically examine the relationship between serum urate and changes in dual-energy CT (DECT) urate volume in people with gout and stable serum urate concentrations.

Methods: Individual participant data were analysed from three studies of people with gout. The time periods for the analysis were selected to identify study participants with serial DECT scans of both feet over a 12-month epoch of stable urate-lowering therapy and serum urate concentrations. Data from 251 study participants were analysed using a mixed models analysis of covariance approach according to mean serum urate cut-points and mean serum urate bands.

Results: For all mean serum urate cut-points assessed (0.24, 0.30, 0.36, 0.42 and 0.48 mmol/L), reductions in DECT urate volumes were observed below the cut-point. Increased DECT urate volumes were observed at or above the 0.48 mmol/L mean serum urate cut-point. Differences in the change in DECT volume were observed for the 0.42 mmol/L cut-point (p=0.0044) and the 0.48 mmol/L cut-point (p<0.0001). Significantly reduced DECT urate volumes were observed for the mean serum urate bands<0.24 mmol/L and 0.24-0.29 mmol/L and increased DECT urate volume was observed for the mean serum urate band≥0.48 mmol/L.

Conclusions: Over 1 year, MSU crystal dissolution, as measured by DECT, occurs with mean serum urate bands of<0.24 mmol/L and 0.24-0.29 mmol/L while MSU crystal formation occurs with mean serum urate≥0.48 mmol/L.