A new approach to the evaluation of hyperphosphatemia in chronic kidney disease

Aims: Hyperphosphoremia, main contributor to cardiovascular calcifications, has a major impact on the morbidity and mortality of chronic renal failure (CRF) patients. Phosphate binders and dietary phosphate limitation are not effective enough to abolish hyperphosphoremia-induced cardiovascular abnormalities, therefore, the identification of other and more timely approaches for serum phosphorous reduction is necessary. Salivary fluid contains phosphate which, if related to the daily salivary secretion (1,000 - 1,800 ml), deserves attention as a marker for an earlier start of pharmacologic treatment for phosphorous removal. In ESRD patients under dialysis we have shown increased salivary phosphate closely to be related with serum phosphorous and interpreted as compensatory. This study evaluates salivary phosphate secretion in 77 nondialyzed CRF compared with healthy subjects and its relationship with renal function. Methods: Saxon's test confirmed normal salivary function in patients and controls. Serum phosphorous, creatinine and GFR were also measured. Results: Salivary phosphorous was significantly higher in CRF patients compared with controls: 38.60 mg/dl (range 12.20-95.60) vs 16.30 (10.30-27.10), p < 0.0001; serum phosphate was also significantly higher: 3.70 (2.10-6.80) vs 3.50 (2.3-4.6), p = 0.013. In CRF patients, salivary phosphorous positively correlated with serum phosphorous (r = 0.45, p < 0.0001) and with serum creatinine (r = 0.72, p < 0.0001), while negatively correlated with GFR (r = -0.72, p < 0.0001). Conclusions: The results of our study show also in CRF patients increased salivary phosphate secretion, which is related with renal function. On this basis the use of salivary phosphate secretion as a marker for an earlier start of the abnormal phosphate metabolism pharmacologic treatment could be proposed.