Gout affects 2-3 out of every 100 people in the UK and causes episodes of painful joint inflammation called flares. These flares occur when crystals of monosodium urate are formed in the joints which form due to the presence of uric acid (or urate) in the blood. It is understood that when the urate levels in the blood rise, there is an increased chance that crystals will form in the joint causing a gout flare. However, serum urate levels are not routinely measured in people without gout and are inconsistently measured in people with gout, so the relationship between urate levels and gout is not fully understood. Also, the chances of having a gout flare is variable throughout the year. It is not known whether this is due to variations in serum urate levels or due to other factors.
This research aims to better understand the relationship between urate levels and gout flares. We will create a cohort of people with gout use routinely collected data to establish when they have a flare of their gout and if they have their serum urate levels measured. We will then describe the relationship between gout flares and serum urate, and how this changes over the year. This will help patients and clinicians better understand gout and when, and why, flares occur.
This study will explore the relationship between gout flares and serum urate levels in an English general practice population. Gout is the most common inflammatory arthritis in the UK there but still uncertainties about its epidemiology and pathophysiology. The relationship between raised serum urate levels and the chances of a gout flare is well established and there is evidence that the incidence of gout flares demonstrates some seasonality. However, the seasonality (or not) of serum urate levels is not well studied.
It is also thought that serum urate levels drop during a gout flare and this is the rationale behind delaying testing of serum urate until 14 days after a flare. We know that serum urate testing is suboptimal, and this time delay may be a barrier to getting serum urate testing done.
This research will aim to establish the relationship between serum urate and gout flares and any seasonality that exists. It will also inform decisions about the timing of serum urate testing in relation to gout flares.
To address this research question, a cohort of incident gout patients will be created. Any subsequent gout flares will be identified using established methods and all serum urate levels will be identified. Patients on urate lowering therapy (ULT) will be excluded and any initiated on ULT will be censored.
The flare rate and seasonality will be described and tested using chi-squared test of fit. Logistic regression will be used to calculate odds ratios for the months of the year with confounder variables of age, sex and ethnicity and rates will be described using these categories. Mean serum urate levels will be similarly described. Urate levels in the 30 days prior to, or post, a gout flare will be illustrated graphically. Rates of urate testing will be described over the study period.
The primary outcomes will be:
1) Gout flares, which will be defined according to criteria previously used in the literature.
2) Serum Urate Levels; latest before index gout episode and all subsequent measurements.
Samuel Finnikin - Chief Investigator - University of Birmingham
Samuel Finnikin - Corresponding Applicant - University of Birmingham
Christian Mallen - Collaborator - Keele University
Edward Roddy - Collaborator - Keele University