RBP4 and gout: RBP4 concentration in the synovial fluid of these patients was between 2.44 and 22.62 μg/mL, with a mean concentration of 11.74 ± 5.85 μg/mL (11.53 ± 2.17 μg/mL in gout patients and 11.94 ± 1.30 μg/mL in CPPD patients).