Calcium and Phosphorus Balance and Calcium Kinetics in Patients With Stage 3/4 Chronic Kidney Disease

The purpose of this study is to gain a better understanding of calcium absorption and
metabolism in patients with Chronic Kidney Disease (CKD). It is important that the body
get enough calcium to support many important body functions including bone health. CKD
changes the calcium balance or how calcium is absorbed and excreted. Because of this, the
knowledge of calcium absorption and excretion in patients with normal kidney function cannot
be used to assess patients with CKD. In patients with CKD bone heath is often negatively
affected due to a combination of poor calcium absorption, increased bone turnover (process
where old bone is removed and new bone is formed), increased level of parathyroid hormone
(PTH [ a hormone that acts to increase calcium in the blood]) and decrease in vitamin D
levels. This negative effect is referred to as Chronic Kidney Disease Mineral Bone Disorder
(CKD-MBD).

Treatment to correct CKD-MBD should begin early in the course of CKD. In the normal
population calcium supplements are frequently used to help prevent age related bone loss.
Calcium supplements can also be used in CKD patients to help bind phosphate. Maintaining
correct levels of phosphate in the body is crucial in CKD. However, calcium supplements may
have adverse effects by promoting calcium phosphate deposits in soft tissues like the
vascular system which could increase the risk of cardiovascular disease.

Therefore this formal balance study is needed to determine if positive calcium balance
occurs in patients with advanced CKD who are given calcium with meals as a phosphate binder.
This study will also evaluate how the body handles phosphate.