Disordered mineral metabolism is not a risk factor for loss of residual renal function in dialysis patients

Abstract

Recent studies showed that mineral metabolism disorders are associated with renal function loss in pre-dialysis patients, but their effects in dialysis patients are less well established. We examined associations between parameters of mineral metabolism and loss of residual renal function (RRF) in dialysis patients. We included 1468 incident haemodialysis (HD) and peritoneal dialysis (PD) patients who were not anuric at dialysis initiation from NECOSAD, a prospective multicentre cohort study. We studied the effects of plasma calcium, phosphorus, calcium-phosphorus product and intact PTH concentrations on loss of RRF. Cox regression models were applied to calculate relative risks of total loss of RRF, defined as anuria during the first 3 years of dialysis. The rate of decline of RRF over time was calculated using general linear mixed models. The mean (SD) age was 59 (15), 62% were men and 59% were treated with HD. We found that both HD and PD patients with the highest phosphorus (P < 0.0001) and calcium-phosphorus product (P < 0.0001) levels had the lowest baseline residual glomerular filtration rate (rGFR) values. During follow-up, 136 HD (15%) and 67 PD patients (12%) became anuric. After adjustment for baseline rGFR, there were no significant associations between parameters of mineral metabolism and the risk of becoming anuric. There were also no differences in the rate of decline in RRF between categories of plasma concentrations. Disordered mineral metabolism was neither associated with the risk of becoming anuric, nor with the rate of decline in RRF in dialysis patients. Differences in decline were mainly attributable to the baseline rGFR value.