Synovial fluid uric acid level aids diagnosis of gout

Examination of urate crystal in synovial fluid (SF) remains the gold standard for diagnosis of gout, but is not universally available. SF uric acid (UA) level may be measured by the uricase method with an automated analyzer. The present study aimed to evaluate the utility of SF to serum UA ratio (SSR) for diagnosis of gout. A cross-sectional study was conducted at the National Center for Rheumatic Diseases, Nepal. Patients presenting with acute (<1 day) joint pain and/or swelling were included. Aspiration was performed in all patients and fluid was subjected to testing for urate level, pH and cell counts and microscopy. Serum samples were also assessed for urate levels, and the SSR was calculated for each patient. A receiver operating characteristic curve was plotted to determine the cutoff value for indicating diagnosis of gout. The difference in SSR between gout and non-gout effusion was evaluated by one-way analysis of variance. A total of 181 patients were included of which 77 had gout. The remaining cases included osteoarthritis, pseudogout, rheumatoid arthritis and ankylosing spondylitis. SSR was significantly higher in gout patients than in any other group (P<0.05). An SSR of ≥1.01 had the highest sensitivity and specificity at 89.6 and 66.3%, respectively, for identifying gout effusion. The present results indicated that SSR may be used as an aid for gout diagnosis when polarizing microscopy is not available.