NEW YORK (Reuters Health) - In patients with rheumatoid arthritis (RA), uric acid is a powerful independent predictor of renal dysfunction and may have a pathogenic role in its development, a study from the UK suggests.
Uric acid's "potential pathogenic role and clinical use as an early biomarker of future renal dysfunction in this group of patients need to be investigated in prospective studies designed specifically for the purpose," Dr. Dimitrios Daoussis from the Dudley Group of Hospitals NHS Trust noted in an email to Reuters Health.
In 350 consecutive patients with RA, Dr. Daoussis and colleagues investigated whether uric acid is associated with renal dysfunction and whether such an association is independent or mediated through other co-morbidities or risk factors for renal impairment.
The investigators assessed and recorded risk factors for renal dysfunction and measured renal function by glomerular filtration rate (GFR).
The mean GFR in the group as a whole was 82.16 ml/min per 1.73 square meters; 116 patients (33%) had a normal GFR (> 90 mL/min), 185 (53%) had mild renal impairment (GFR, 60-90 mL/min) and 49 (13%) had moderate renal impairment (GFR < 60 ml/min). No patient had severe renal impairment.
The mean uric acid level for the cohort was 310.9 umol/L; only 31 subjects were hyperuricemic -- defined as uric acid levels greater than 500 umol/L for men and greater than 400 umol/L for women.
According to their report in the July 24 online issue of Arthritis Research and Therapy, uric acid was strongly inversely associated with GFR (p < 0.001) in univariate analysis. Other variables found to have significant associations with GFR were age, systolic blood pressure, total cholesterol, triglycerides, and RA duration.
In multivariate analysis, uric acid, regardless of the presence of hyper- or normo-uricemia, was the strongest predictor of renal dysfunction (p < 0.001) "and was independent from all the traditional risk factors for cardiovascular or renal disease," Dr. Daoussis reported to Reuters Health.
Adjustments for the use of medications (diuretics, low dose aspirin, COX-II inhibitors and NSAIDs), and further adjustment for markers of inflammation and insulin did not alter the results.
This association was not present in patients with normal renal function, the investigators note.
"Therefore, uric acid may indeed play a direct pathogenic role in the development of renal dysfunction in RA," Dr. Daoussis concluded.
Arthritis Res Ther 2009;11:R116.