Rheumatologists in Australia and New Zealand have characterised the prevalence of incident clinically evident gout in people with low-normal baseline serum urate (SU) concentrations in findings that could have implications for determining population risk.
An elevated serum uric level is a known risk factor for developing gout but little is known about the prevalence of incident cases over time in people with lower levels, say investigators led by Associate Professor Philip Robinson from the University of Queensland and the Royal Brisbane and Women’s Hospital.
Their analysis of four large longitudinal cohorts – the Atherosclerosis Risk in Communities Study (ARIC), Coronray Artery Risk Development in Young Adults Study (CARDIA), and both the Original and Offspring cohorts of the Framingham Heart Study (FHS) – shows that while a baseline serum urate level of 5.50 mg/dL or more is a risk factor for development of gout, the disease can sometimes occur in a proportion of people – 0.59–3.2% – with lower levels
The study includes individual patients data from 18,889 participants who were gout-free at baseline with the incidence of gout calculated over time at three, five,10, 12 and 15 years.
Researchers say there was no clear pattern of increase in incident gout in the entire cohort and across all time periods until 6mg/L where incidence ‘clearly increased from the lower urate levels and dramatically increased’ in the > 7 mg/dL band.
The incidence of gout at 15 years with a baseline serum urate < 4.00 mg/dL was 0.59% but for subsequent urate bands between 4.00 mg/dL to 5.99 mg/dL, investigators described a largely static incidence of gout.
For participants with baseline serum urate of 6.00 mg/dL to 7.00 mg/dL the incidence rose more sharply to 2.9% for 6.00–6.49 mg/dL and 3.2% for participants with baseline serum urate of 6.50–6.99 mg/dL.
Meanwhile, in participants with baseline serum urate > 7.00 mg/dL, the 15 year incidence was 12.2% – a risk that persisted regardless of gender although investigators did observe differences in the pattern of risk according to baseline SU levels in males and females.
In males there was higher risk for serum urate level bands between 6.00 mg/dL and 6.99 mg/dL, and significantly higher risk for serum urate > 7.00 mg/dL. In contrast, for females, virtually all of the serum urate level bands had an increased risk.
While noting that the reason for the difference remains unclear, the investigators speculated that it could reflect the fundamental differences in the pathogenesis of gout between men and women, at least at lower urate levels’
“The difference seen in the female groups (less than and greater than 50 years of age) may well be related to menopausal status. Oestrogen is uricosuric and the loss of oestrogen after menopause may explain the change in incident gout risk seen between the two female age groups.”
The study was published in BMC Rheumatology.