Clearance of osteocalcin by peritoneal dialysis in children with end-stage renal disease

Osteocalcin is a bone-specific protein whose concentration in blood is a direct reflection of bone turnover. In chronic renal failure, circulating osteocalcin is elevated. This elevation is due to decreased renal clearance and, in some patients, increased bone turnover secondary to renal osteodystrophy. In children receiving continuous ambulatory peritoneal dialysis, mean serum osteocalcin concentrations are substantially lower than in similar patients on hemodyalysis (1). This difference may be due to clearance of the protein by the peritoneal membrane. To test this possibility we examined osteocalcin in 16 infants and adolescents undergoing continuous ambulatory peritoneal dialysis with two commercially available glucose-based dialysis solutions (2.5 and 4.25% Dianeal). Mass transfer of osteocalcin over 5-h dialysis exchange periods was -18.9 +/- 2.8 and -28.4 +/- 7.8 micrograms for the low and high glucose solutions, respectively. Serum levels fell over the course of single exchange periods in concert with increasing dialysate concentrations. There were significant correlations between initial blood concentrations of osteocalcin and the total amount of osteocalcin transferred (r = 0.609 and 0.642 for the high and low glucose solutions, respectively, p less than 0.05). There were also strong correlations between the mass transfers of osteocalcin and those of creatinine (p less than 0.05) and total protein (p less than 0.01) with the 4.25% glucose exchange. The relationships were weaker with the 2.5% glucose exchange. Fractionation of serum revealed a single immunoreactive peak eluting coincident with intact osteocalcin, but two or three immunoreactive peaks were identified in matching dialysate samples, suggesting that both intact osteocalcin and circulating fragments are transferred by the peritoneal membrane.(ABSTRACT TRUNCATED AT 250 WORDS)