Quantifying exposure to calcium and phosphate in ESRD; predictive of atherosclerosis on top of arteriosclerosis?

Background: Long-term exposure to hypercalcaemia and hyperphosphataemia leads to media calcification and predicts mortality in patients with end-stage renal disease (ESRD). It is debatable whether this exposure is only a risk factor for arteriosclerosis, or also for superimposed atherosclerosis. Calcium-phosphate exposure is difficult to quantify, because it is variable in time and exerts its deleterious effects only after prolonged presence. Methods: In 90 dialysis patients, calcium and phosphate values from the complete dialysis period were collected. From three-month averages, measures for calcium-phosphate exposure were derived after exclusion of transplant periods. Calcium-phosphate exposure was then related to intima-media thickness (IMT) and to ankle-brachial index (ABI) as markers of early atherosclerosis. Results: Calcium-phosphate exposure was quantified in three ways using 1670 patient-quarters (i.e. three-months periods) covering 93% of the time on dialysis: averaged calcium-phosphate exposure, percentage of time with above-reference values, and burden of hypercalcaemia/hyperphosphataemia represented by this percentage multiplied by months on dialysis. No association was found with IMT. Patients with increased, not decreased, ABI had higher calcium-phosphate exposure throughout dialysis treatment: hyperphosphataemia burden was 31 (19 to 43) months for patients with ABI between 0.90 and 1.40 and 79 (58 to 100) months for patients with ABI >1.40 or incompressible ankle arteries (p