Salivary phosphate secretion in chronic kidney disease

Hyperphosphatemia is an important contributor to cardiovascular calcification in chronic renal failure (CRF) patients. Cardiovascular calcifications are responsible for the high morbidity and mortality in patients undergoing hemodialysis (HD). Despite dietary phosphate reduction and treatment with phosphate binders, serum phosphorus level, as recommended by K/DOQI guidelines, is achieved only by 50% of dialysis patients. Thus it is necessary to identify other therapeutic approaches to reducing serum phosphate. Phosphate may be secreted in the saliva, which is then swallowed, and this provides a source of endogenous phosphate and thus contributes to the hyperphosphatemia in CRF.

This study evaluated salivary phosphate in 68 HD patients and 110 subjects with various degrees of CRF, compared with 30 healthy subjects. Saxon's test confirmed normal salivary secretion volume in all subjects. Salivary and serum phosphate and calcium and serum parathyroid hormone were measured.

Both HD and CRF patients had significantly higher salivary phosphate levels compared with healthy control subjects. In the latter group of patients, salivary phosphate correlated positively with serum creatinine (P < .0001) and the glomerular filtration rate (P < .0001).

These results suggest that the level of salivary phosphate may provide a better marker than serum phosphate for the initiation of treatment of hyperphosphatemia in CRF and HD patients. The results may also offer a new horizon in the therapy of hyperphosphatemia by establishing measures to bind salivary phosphate in the mouth, and before saliva is swallowed.