Peritoneal dialysis clearances. A practical approach to the measurement of small- and middle-molecule clearances.

This study was designed to (1) develop a simple technique of estimating 'middle-molecule' clearances in peritoneal dialysis patients using vitamin B12 as a marker; (2) evaluate changes in small- and middle-molecule clearances during a single 24- or 36-hour peritoneal dialysis, and (3) determine if using 4.25% rather than 1.5% dextrose exchanges alters the clearances of small and middle molecules. Measurement of clearance following the intramuscular injection of vitamin B12 was found to be a reliable method of estimating the clearance of middle molecules. Small- and middle-molecule clearances remain constant throughout an individual 24- or 36-hour dialysis. In addition, small-molecule clearances increase significantly with 4.25% dextrose dialysate but return to prior values when 1.5% dextrose dialysate is reinstituted.