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

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.

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.

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).

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.