Since our TPE procedure uses acid-citrate-dextrose solution A infusion to bind ionized calcium for regional anticoagulation in the circuit, and involves calcium gluconate infusion in the return line to avoid systemic symptomatic hypocalcemia (5), we hypothesized that calcium and PTH would remain stable while TPE would acutely decrease the concentrations of phosphate and FGF-23. Here, FGF23 is linked to Hypocalcemia.