Calcium and Vitamin D in CKD

A calcium result is a physiologic signal, not a diagnosis. The useful question is how kidney function, phosphate, PTH and vitamin D are interacting to produce that result. In CKD, phosphate retention and reduced renal vitamin D activation can produce hypocalcemia or a low-normal calcium concentration, which stimulates secondary hyperparathyroidism. The same patient may later develop hypercalcemia from treatment, autonomous parathyroid disease or another cause. The safe approach is therefore pattern-based: establish whether the calcium is truly abnormal, identify the direction of PTH and phosphate change, and then match treatment to CKD stage and dialysis status. This lesson uses Canadian laboratory conventions: calcium is usually reported in mmol/L and 25-hydroxyvitamin D in nmol/L. Canadian NPs apply provincial or territorial prescribing authority, formularies and local renal protocols; dialysis-related CKD-MBD decisions commonly require nephrology collaboration.