Variability in creatinine clearance (CCR) and KT/V due to different methods of calculating volume and CCR.

OBJECTIVE

This study aimed to compare the correlations between KT/V and creatinine clearance (Ccr) calculated by different methods and to determine and compare the correlations between KT/V and Ccr.

DESIGN

Nonrandomized, retrospective analysis of data.

SETTING

Continuous ambulatory peritoneal dialysis (CAPD) outpatient clinic in a teaching hospital.

PATIENTS

All patients were included for analysis if the data collection was complete for the calculations of KT/V and Ccr using five different methods.

INTERVENTIONS

Volume of distribution for urea (V) was estimated by four methods: Watson nomogram, ideal body weight (IBW), actual body weight, and total body surface area. Ccr was determined by five methods: Dialysate Ccr was calculated by creatinine (Cr) uncorrected and corrected for the presence of glucose; urinary Ccr was calculated using urinary Cr alone and the average urinary clearance of urea and Cr; and by the Cockcroft and Gault method.

MAIN OUTCOME MEASURES

Correlations between KT/V and Ccr.

RESULTS

Sixty-three data sets were collected from 52 CAPD patients. The correlations between weekly KT/V and Ccr normalized to 1.73 m2 body surface area were found to be highly variable from one method to another (r2 = 0.012 -0.494). For obese patients (20% above IBW), KT/V values obtained were more variable using the Watson nomogram compared to the IBW and BSA methods.

CONCLUSION

KT/V calculated using the Watson nomogram and the Ccr determined using average of urinary urea and creatinine clearance gave the best correlation (r2 = 0.49).