Serum urate as a soluble biomarker in chronic gout-evidence that serum urate fulfills the OMERACT validation criteria for soluble biomarkers

Objectives: To determine whether serum urate (SU) fulfills the Outcome measures in Rheumatology (OMERACT) soluble biomarker criteria.

Methods: The OMERACT soluble biomarker criteria were adapted for use in chronic gout. Potential outcome measures for use in chronic gout were identified. The literature was reviewed to determine which of the potential outcome measures were appropriate and whether there was evidence within the current literature to fulfill the OMERACT biomarker criteria.

Results: The assay for measurement of SU is reliable, internationally standardized, and readily accessible for use in clinical practice. The effects of sources of variability, including age, sex, ethnicity, circadian rhythms, body mass index, renal/hepatic function, and fasting, are well documented. Tophus regression was identified as appropriate structural outcome measure; however, given that not all patients have clinically apparent tophi, the number of gout flares is also identified as a key outcome measure.

Conclusions: Serum urate fulfills all the OMERACT biomarker criteria with the exception of its effects on outcome measures. Further analysis of existing and new data sets to determine whether a reduction in SU predicts a reduction in gout flares, the number/size of tophi, and patient reported outcomes using validated measures for these outcomes are required.