Monocytic expression of GPR68 mRNA and serum retinol levels in CKD patients with a BNP level >100 pg/mL were significantly higher than those in healthy subjects with a BNP level under 40 pg/mL (P < 0.05 for GPR68 mRNA, P < 0.01 for retinol, Fig. 8i). This evidence concerns the gene NPPB and chronic kidney disease.