Development of gout in people with asymptomatic hyperuricemia: study protocol for a 5-year prospective cohort

Introduction The central biochemical cause of gout is hyperuricemia (elevated serum urate levels). Ultrasound features of monosodium urate (MSU) crystal deposition are common in people with asymptomatic hyperuricemia. However, it is unclear whether this is a precondition for the development of gout. This study aims to determine whether ultrasound imaging evidence of MSU crystal deposition predicts development of symptomatic gout over 5 years, in people who already have an increased risk of gout due to elevated serum urate concentrations (≥8 mg/dL).Methods and analysis This is a prospective, international, multicentre study. The study population comprises over 250 participants with asymptomatic hyperuricemia (serum urate ≥8.0 mg/dL). After the baseline assessments, participants are followed for 5 years or until the development of gout, defined by the 2015 American College of Rheumatology/European Alliance of Associations for Rheumatology gout classification criteria. Baseline assessments include anthropomorphic measures, laboratory tests, questionnaires, blood and urine specimen collection, plain radiographs of the feet and standardised ultrasound scans of the lower limbs, scored according to the Outcomes in Rheumatology (OMERACT) gout ultrasound scoring system. The primary outcomes are the development of gout and time course for development of gout in people with and without ultrasound evidence of MSU crystal deposition. Exploratory analyses will examine clinical, genetic and biological factors associated with development of MSU crystal deposition and gout.Ethics and dissemination This study protocol was approved by the New Zealand Ministry of Health Southern Health and Disability Ethics Committee (MEC/05/10/130/AM16) on 18 December 2018. The findings from this study will be published in peer-reviewed journals and will be presented at national and international conferences.Trial registration number ACTRN12619000915156.