Patient-reported gout attack frequency and allopurinol use in general practice in the Netherlands: a prospective observational cohort study protocol

INTRODUCTION: Gout is the most common inflammatory arthritis in the Dutch general practice population and is often managed with long-term uric acid lowering treatment. The clinical relevance of this treatment in preventing gout attacks is unclear. PRIMARY RESEARCH QUESTION: What is the frequency of self-reported gout attacks and what is the effect of allopurinol use in patients diagnosed with gout in general practice? METHODS AND ANALYSIS: Adult patients with a diagnostic consultation code for gout in the year 2013, 2014 or 2015 will be invited to participate in this prospective observational cohort study. Patients with a limited life expectancy will be excluded. Baseline measurements will include blood pressure, body mass index and a blood sample (estimated glomerular filtration rate, serum uric acid, cholesterol (low-density lipoprotein (LDL) and high-density lipoprotein), glucose (fasting)). At the 2-year follow-up, patients will receive questionnaires every 3 months. The questionnaires at baseline, 12 months and 24 months assess the frequency of gout attacks, the presence of tophi, comorbidity, medication use, quality of life, diet and lifestyle. The questionnaires in between only assess the frequency of gout attacks and medication use for gout. Descriptive statistics will be used to calculate the mean frequency of self-reported gout attacks during the 2-year follow-up. The propensity score for each patient being offered allopurinol is estimated and used to match patients with and without allopurinol treatment. We will compare the frequency of gout attacks in these groups using multilevel Poisson regression analyses. With this type of analysis, we can calculate the corrected estimated effect of allopurinol on gout attack frequency. ETHICS AND DISSEMINATION: The research protocol was approved by the Medical Ethical Committee of the Erasmus Medical Centre in Rotterdam. The knowledge generated by this study will be transferred to the Dutch College of General Practitioners, conferences and to (inter)national peer-reviewed journals. TRIAL REGISTRATION NUMBER: NTR6329; Pre-results.