Day-to-day variability of adequacy indexes in peritoneal dialysis

Serum β2-microglobulin as a predictor of residual kidney function in peritoneal dialysis patients

BACKGROUND

While clinical guidelines recommend that residual kidney function (RKF) is measured in peritoneal dialysis (PD) patients, 24-h urine collection is cumbersome and prone to errors. We wished to determine whether an equation using serum β2-microglobulin (β2M) could prove of clinical benefit in estimating RKF and identifying patients who could start PD with incremental prescriptions.

METHODS

We measured serum β2M in consecutive PD outpatients recently starting dialysis with continuous ambulatory PD (CAPD) or automated PD (APD), attending a single tertiary hospital for their routine clinical visit. RKF was defined as the mean of 24-h urine clearances of creatinine and urea. An equation estimating RKF (eRKF) was generated based on serum β2M levels on a randomly selected modelling group.

RESULTS

We included 511 patients, of whom 351 in the modelling group and 150 in the validation group. Mean age was 58.7 ± 15.8, 307 (60.0%) were men and median RKF value was 4.5 (2.4-6.5) mL/min/1.73 m2. In the validation group, an equation based on β2M, creatinine, urea, age and gender showed minimal bias of - 0.1 mL/min/1.73 m2 to estimate RKF. Area under the receiving operator characteristic curve was 0.915 to detect RKF ≥ 2 mL/min/1.73 m2.

CONCLUSION

An equation based on serum β2M concentration would not be able to replace 24-h urine collection as the standard of care when an exact measurement of RKF is required. However, it could prove useful in identifying patients suitable for an incremental PD prescription and for monitoring RKF in individuals unable to reliably collect urine.

Derived equations are not precise enough to predict the adequacy of creatinine clearance in peritoneal dialysis patients

BACKGROUND

Most renal units assess dialysis adequacy in peritoneal dialysis (PD) patients by formal 24-hour collections of urine and effluent dialysate. We sought a reliable method of predicting dialysis adequacy that allows a decrease in the frequency of these formal and cumbersome measurements.

METHODS

We created a formula for estimating total creatinine clearances, then assessed the clinical utility of this formula and other published formulae in predicting adequate and inadequate dialysis in PD patients. We collected data over a 6-month period in 2001 from 288 PD patients from 9 centers in Scotland. Four out of every 5 patients were selected at random to create a formula for estimating total creatinine clearance per week, and the fifth patient was used to form a validation group. We plotted creatinine excretion against age, and the resultant linear regression equation was transformed to produce a formula for predicting total creatinine clearance per week, based on patient sex, weight, and serum creatinine. We used the data from the validation subgroup to calculate predictive values for our derived formula and data from all of the patients to calculate predictive values for the Cockcroft and Gault, Jones, and Modification of Diet in Renal Disease Study formulae.

RESULTS

Neither our derived formula nor the three published formulae were sufficiently powerful to predict accurately either adequate or inadequate PD clearance. Receiver operator characteristic curves showed that no significant improvement in these predictive values could be achieved by altering either the sensitivity or the specificity.

CONCLUSION

Prediction formulae are not accurate enough to detect underdialysis in PD patients.