RBP4 and Insulin resistance: Several authors have therefore proposed to use the retinol:RBP4 ratio rather than RBP4 levels alone as a better marker (a low retinol:RBP4 is associated with insulin resistance), suggesting that retinol-free RBP4 (apo-RBP4) might contribute more to insulin resistance than retinol-bound RBP4 (holo-RBP4) [15,16].