Errors Involved in the Application of an Imperfect Peritoneal Volume Marker

Abstract

Peritoneal volume markers have been used in numerous studies on fluid transport in peritoneal dialysis. The basic assumption used was that the macromolecular marker was stable and that the free fraction of a label (usually radiolabel) was negligibly small. In this study are presented theoretical investigations on the errors involved in application of an imperfect volume marker containing free fraction of a label. These investigations were used in assessing the errors in calculation of peritoneal volume time course, V, and fluid absorption rate (estimated by volume marker clearance, kE) using data from 20 clinical dwell studies with 1.36% Dianeal dialysis solution and radioiodinated human serum albumin as a volume marker. It has been shown that with an in vitro measured 125I free fraction of 2.72%, the error of kE estimation was 11%. However, the maximal error in estimation of V was only 0.2%. In conclusion, the performed analysis implies that calculation of the peritoneal volume time course during the dwell (with correction for the volume marker elimination) is very reliable, and the existence of a free fraction of a volume marker label results in a negligibly small error. However, even small free fraction of the label results in a significant overestimation of the fluid absorption rate.

Erythrocytes as Volume Markers in Experimental PD Show that Albumin Transport in the Extracellular Space Depends on PD Fluid Osmolarity

“…The current results support the presence of sieving effects that slow down the uptake of cells in relation to that of fluid in the peritoneum as a whole. Lymphatic elimination at a known stable rate should not, however, constitute an obstacle for the application of erythrocytes as a volume marker (28). Hypothetically, direct uptake of labeled albumin from the tissue to blood may increase its concentration in blood, mimicking lymphatic uptake.…”