LRP2 and chronic kidney disease: Serum calcitriol concentration could be normalized following vitamin D supplementation achieved by a 2-fold increase in calcitriol production when more calcidiol substrate was provided.134 Standard doses used for vitamin D replacement (to achieve a targeted calcidiol level) often do not achieve targeted concentration in people with CKD due to reduced megalin expression in the proximal tubules and the above mentioned loss of calcidiol to the urine.10