Normalised cellular clearance of creatinine, urea and phosphate

The observation of a significant postdialysis rebound in the serum concentration of small molecules demonstrates the existence of a limited cellular clearance (KC). Theory suggests that KC is proportionate to weight, and it is therefore more rational in interindividual comparisons to measure the normalised cellular clearance (KCn). Both variables can be determined from the shape of the rebound curve. KC and KCn were determined in 34 maintenance dialysis patients on two occasions, obtaining the following values: KC urea 502 ± 179 ml/min, KCn urea 7.80 ± 2.42 ml/kg/min, KC creatinine 394 ± 141 ml/min, KCn creatinine 6.03 ± 1.42 ml/kg/min, KC phosphate 369 ± 132 ml/min, KCn phosphate 5.62 ± 1.24 ml/kg/min. KC was significantly correlated to weight for all three substances, but no correlation was seen between KCn and weight, height, age, sex, uremia duration or dialysis duration. KCn urea was significantly higher that KCn creatinine and KCn phosphate. KC urea was substantially lower than previously published figures, suggesting that some dialysis patients may be underdialysed due to overestimation of KT/V using conventional single-compartment urea kinetic modelling.