Time to redefine hyperuricemia? The serum uric acid cut-off level for precipitation might be lower: a pilot study.

Background: Hyperuricemia is classically defined as serum uric acid (SUA) value higher than 6.8 mg∕dL; between hyperuricemic patients, only 15-20% will develop gout. Our first goal was to find if there is a specificity of the "snowstorm" feature on ultrasound (US) for hyperuricemia. Moreover, we aimed to determine if there is a level of SUA from which the urates tend to appear in the synovial fluid, without generating a typical clinical gouty flare.

Patients, materials and methods: We conducted a cross-sectional, transverse study, including 108 consecutive patients that displayed a set of clinical and imaging features, such as swollen knee and US proof for knee joint effusion.

Results: Performing binary logistic regression, the relation between the explanatory variable (hyperechogenic spots) and the response variable (SUA) was demonstrated to be a significant one (p=0.005). The value of 0.397 for the statistical phi coefficient suggests a medium intensity association between the diagnosis of gout or asymptomatic hyperuricemia and whether the patients have hyperechogenic spots or not. We found the cut-off value for SUA equal to 4.815 mg∕dL, regardless of gender, from which, the urate starts to precipitate. Values for men tend to be higher in comparison to the ones found for women (4.95 mg∕dL vs. 3.9 mg∕dL).

Conclusions: The "snowstorm" aspect of the fluid might be the result of an increased level of SUA and more than this, the cut-off level for SUA to precipitate might be lower than the fore used values.