RBP4 and arthropathy: Additionally, we noticed that synovial fluid leukocyte count, a well-known marker of inflammation for this type of arthropathy, correlated negatively with serum uric acid levels (Figure 1D) and also with synovial RBP4 levels (Figure 1E), although no significant correlation was found between uric acid and RBP4 levels (Supplementary Figure S2).