RBP4 and type 2 diabetes mellitus: Some discrepancies involve the lack of elevated Rbp4 expression in the adipose tissue of obese patients reported by some studies [151] and the dependence of serum RBP4 concentrations on renal filtration, which is known to decline with type 2 diabetes and may actually be the underlying reason for elevated RBP4 levels in these subjects [152,153].