SINGLE COMPARTMENT MODELS FOR EVALUATING BETA(2)-MICROGLOBULIN CLEARANCE DURING HEMODIALYSIS

Methods for evaluating dialyzer clearance of beta(2)-microglobulin dur ing clinical hemodialysis have not been well established. The authors show, theoretically, that the postdialysis-to-predialysis concentratio n ratio, a parameter often used to estimate dialyzer clearance of beta (2)-microglobulin, depends on KdT/V (the dialyzer clearance times the treatment time divided by the distribution volume for beta(2)-microglo bulin) and the ultrafiltration rate, assuming that a single compartmen t kinetic model is valid. They also show that adjustment of the postdi alysis concentration of beta(2)-microglobulin for changes in its volum e of distribution does not entirely correct for fluid removal when the adjusted postdialysis-to-predialysis concentration ratio is significa ntly below one. These considerations suggest that estimates of dialyze r clearance of beta(2)-microglobulin using single compartment models a re more reliable than those using only the postdialysis-to-predialysis concentration ratio. To illustrate these constructs, the authors comp ared experimental estimates of beta(2)-microglobulin clearance during clinical hemodialysis using single compartment models with those measu red directly from the arteriovenous concentration difference across th e dialyzer. First-use low flux and high flux dialyzers and those repro cessed with Renalin were studied. single compartment estimates of beta (2)-microglobulin clearance for low flux dialyzers were similar to tho se measured directly across the dialyzer, but single compartment estim ates of beta(2)-microglobulin clearance for high flux dialyzers exceed ed (p < 0.001) those measured directly across the dialyzer, independen t of whether fluid removal during hemodialysis was assumed to be remov ed entirely from the extracellular compartment or proportionally from both intracellular and extracellular compartments. The authors conclud e that accurate estimates of beta(2)-microglobulin clearance for high flux dialyzers will require kinetic models that are more complex than those assuming a uniform distribution of beta(2)-microglobulin in a si ngle, well-mixed compartment.