PTH and chronic kidney disease: In summary, the present results demonstrated a significantly negative association of urinary C-megalin excretion with serum 25(OH)D, 1,25(OH)2D and 24,25(OH)2D, and positive associations with 1,25(OH)2D/25(OH)D and 1,25(OH)2D/24,25(OH)2D, in addition to the established roles of PTH and FGF23 in 25(OH)D metabolism, even in pre-dialysis CKD patients.