Soluble urate in sera and synovial fluids from patients with different joint disorders

To evaluate simultaneous serum and synovial fluid (SF) urate levels in various inflammatory and noninflammatory joint disorders and to correlate SF white blood cell (WBC) counts with serum and joint fluid urate levels.

Sixty-three paired samples of sera and SF from 58 patients including 25 patients with inflammatory arthropathies, 18 patients with gout and 15 patients with noninflammatory joint disorders, were measured for urate concentrations by a UV enzymatic method.

In inflammatory arthropathies other than gout, urate concentrations in SF were significantly lower than in paired sera (p < 0.0001). There was no difference between the SF and serum urate levels in noninflammatory arthropathies and in gout. In gout, however, SF urate occasionally were found to be considerably higher than in sera. This phenomenon was observed in fluids with massive amounts of monosodium urate crystals. There was no correlation between SF WBC counts and serum of SF urate levels in any of the disease groups studied.

Serum and synovial fluid levels vary more than previously recognized. SF urate levels tend to reflect serum levels in gout and noninflammatory arthropathies but not in inflammatory joint disorders. Disturbed purine metabolism in inflammatory arthropathies may reflect a component in the pathophysiology of inflammation. The elevations of SF urate levels seen in gout are unique for this disease and most likely reflect crystal dissolution in joints.