Chronic kidney disease, in its later stages, may cause hyperphosphatemia. Hyperphosphatemia promotes the bone resorption and tend to increase the amount of calcium in vessels and increases the risk of vascular calcification. Parathyroid hormone also increases in chronic kidney disease which also promotes bone resorption, hypercalcemia, and vascular calcification. Vitamin D 3, if given in a patient who has hyperphosphatemia, may actually promote bone resorption and vascular calcification if PTH is more than 100. So if there is hyperphosphatemia, vitamin D should be given along with a phosphate binder such as sevelamer if the calcium-phosphate product is more than 55.

If Calcium phosphate product is more than 55, it means you shouldn't give calcium-based phosphate binders such as calcium acetate, instead start the patient on Sevelamer. But if Calcium phosphate product is less than 55 then give patient calcium acetate as a phosphate binder. Decide the dose of vitamin D based on PTH level. If it is more than 100 give activated form of vitamin D which is 1-25 dihydroxy vitamin D3.

For example, if a patient has corrected calcium (How to calculate corrected calcium for hypoalbuminemia?) of 10.5 and phosphate of 5.5, then his calcium phosphate product will be (10.5 x 5.5) 57.75. So we will start the give sevelamer to the patient as a phosphate binder.

Summary: 

If Calcium phosphate product is > 55 give Sevelamer as a phosphate binder. 
If Calcium phosphate product is < 55 give Calcium acetate as a phosphate binder. 
If PTH is more than 100 give activated form of vitamin D. 


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