#1250 Measurement of ionized calcium with a point-of-care ionometer during treatment with etelcalcetide

Abstract Background and Aims Etelcalcetide is an intravenous calcimimetic indicated for the treatment of mineral and bone disorders in hemodialysis patients by lowering parathyroid hormone (PTH), calcium and phosphorus. The assessment of ionized calcium versus total calcium has not yet been studied during treatment with etelcalcetide, and there are no real data on the occurrence of hypocalcemia as measured by ionized calcium in the pre- and post-hemodialysis period during treatment with etelcalcetide. The aim of this study was to describe the time course of ionized and total serum calcium levels during chronic treatment with etelcalcetide and to assess the occurrence of hypocalcemia in patients treated with etelcalcetide by measuring ionized calcium levels. Method This was an observational, non-interventional, prospective, single-arm phase IV study. A total of 20 chronic hemodialysis patients (15 men and 5 women) aged 55.9 ± 18.2 years undergoing dialysis for 5.5 ± 4.3 years in two hemodialysis centers of the University Medical Centre Ljubljana were enrolled in the study between January 2020 and March 2021. All patients received etelcalcetide as a bolus injection into the venous line of the dialysis circuit three times a week, immediately after each hemodialysis session. Ionized calcium levels were determined using a point-of-care ionometer (GEM Premier 3000) before starting treatment with etelcalcetide prior to dialysis, then during treatment in the first week before and after dialysis, then once a week until the maintenance phase was reached and at least once a month thereafter. Hypocalcemia was defined by a pre-dialysis ionized calcium concentration below 0.90 mmol/L. The corrected total calcium values was measured prior to dialysis at least once a month according to routine clinical practice. The data of all these patients were included in the analysis, except for one, who underwent a kidney transplantation after receiving only 4 doses of etelcalcetide. Results We demonstrated that both corrected total calcium and ionized calcium before dialysis decreased over time during treatment with etelcalcetide. Of 240 measurements of ionized calcium with a point-of-care ionometer at the bedside, the concentration of ionized calcium was below 0.90 mmol/L three times in two patients (0.81, 0.84, 0.85). In one patient, we increased a calcium level in the dialysate from 1.50 to 1.75 mmol/L and in the other from 1.25 to 1.50 mmol/L. In addition, we observed 2 further measurements of ionized calcium of 0.90 mmol/L and 18 measurements between 0.91 and 0.96 mmol/L. However, this corresponds to 1.25% of hypocalcemias with ionized calcium below 0.90 mmol/L and 8.3% of those with calcium between 0.90 and 0.96 mmol/L. As calcium concentration in the bath increased, the pre-dialysis calcium concentrations also appeared to increase. At the beginning of the study, the calcium concentration in the dialysate was 1.5 mmol/L in 16 of 20 patients. 2 patients were treated with a calcium concentration in the dialysate of 1.75 mmol/L and 2 others with 1.25 mmol/L. The proportion of patients using higher dialysate calcium concentration was higher at the end of the study, as two patients switched to 1.75 mmol/L, and one from 1.25 to 1.50 mmol/L. This probably indicates a co-intervention triggered by a reduction in serum calcium levels prior to dialysis during treatment with etelcalcetide. Visual comparisons of the time course of ionized and corrected calcium concentrations before dialysis during chronic treatment with etelcalcetide in 19 patients showed a good correlation between point-of-care ionized calcium and routinely measured total calcium. Conclusion A point-of-care ionometer for the determination of ionized calcium at the bedside has the potential to guide etelcalcetide therapy by optimizing serum calcium levels and also to prevent potentially threatening hypocalcemia.