Clinical efforts to get patients with a history of gout to reach specific target serum urate (SU) levels less than either 5 or 6 mg/dL could prevent the great majority of gout flares and hospitalizations for them, according to a new study that tracked patients for a mean of 8.3 years.
The findings, which appeared February 6 in JAMA, “support the value of target serum urate levels in gout flare prevention in primary care, where most gout patients are treated,” rheumatologist and study coauthor Hyon K. Choi, MD, DrPH, of Harvard Medical School and Massachusetts General Hospital, Boston, told this news organization. However, Dr. Choi noted that “the value of relying on target urate levels is not accepted in primary care practice,” and the author of an accompanying commentary said that the jury is still out about the best strategy to prevent flares.
Dr. Hyon K. Choi
Gout is caused by monosodium urate crystallization within the joints, which occurs when SU levels exceed the saturation point for uric acid crystallization in the body: approximately 6.8 mg/dL. “Studies have found strongly graded associations between serum urate levels above the saturation point and the risk of developing new cases of gout among individuals without gout at baseline,” Dr. Choi said. “However, associations between serum urate levels and the risk of recurrent flares among preexisting gout patients, which is relevant to clinical gout care practice, has not been established.”
Dr. Choi added that “despite the emphasis in US and European rheumatology guidelines on the use of urate-lowering therapy to treat-to-target serum urate level — eg, under 6 or 5 mg/dL — the proportions of flares associated with such target urate levels remained unknown.”
Study Shows Relationship Between SU Levels and Recurrent Flares
For the study, researchers tracked 3613 patients aged 40-69 with gout in the UK Biobank database from 2006-2010 to 2017 or 2020. The patients, 86% of whom were men, had a mean age of 60 years and about 96% were White.
Among the patients, 1773 new episodes of acute gout occurred in 27% of the patients (16% had one episode, 6% had two episodes, and 5% had at least three episodes). These were treated in primary care or required hospitalizations. The other 73% of patients had no new acute gout episodes.
Overall, 95% of flares occurred in those with baseline SU levels ≥ 6 mg/dL, and 98% occurred in those with levels ≥ 5 mg/dL.
Patients with baseline SU levels < 6.0 mg/dL had an acute gout flare rate of 10.6 per 1000 person-years. In comparison, relative risks for acute gout flares per 1000 person-years were 3.16 at baseline SU levels of 6.0-6.9 mg/dL, 6.20 for 7.0-7.9 mg/dL, 7.70 for 8.0-8.9 mg/dL, 9.80 for 9.0-9.9 mg/dL, and 11.26 for > 10 mg/dL after adjustment for various possible confounders (P < .001).
The researchers identified 64 hospitalizations with gout as the main discharge diagnosis, and 97% occurred in patients with baseline SU levels ≥ 6 mg/dL. All were in patients with baseline SU levels ≥ 5 mg/dL.
“An important feature of this study was that serum urate measurements were obtained from all gout patients at the study baseline, irrespective of clinical needs or flare status,” Dr. Choi said. “Prior studies failed to reveal the truly compelling nature of relations between serum urate levels and recurrent flares among preexisting gout patients.”
As for the cost of SU tests, Dr. Choi said they can run as low as $2. “Portable tests similar to home glucose measurement for diabetes patients are also being adopted by certain gout care practices,” he said.
The findings matter, Dr. Choi said, because SU is not tracked in the “vast majority of gout patients” in primary care. Instead, primary care doctors — as per the guidelines of the American College of Physicians — often adopt an approach that treats symptoms as needed instead of tracking and lowering SU levels, he said. In fact, “95% and 98% of gout flares can be potentially preventable at the population level if serum urate levels < 6 and < 5 mg/dL can be met, respectively, and 100% of hospitalizations for gout could be preventable with serum urate < 5 mg/dL,” he said.
As for limitations, the authors noted that participants in the UK Biobank “typically have a better socioeconomic status and are healthier than the UK general population,” and they added that “these data may underestimate the number of acute gout flares in the cohort.” Also, 55% of the total 502,490 patients in the UK Biobank were excluded owing to lack of primary care data.