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Predicted and measured daily creatinine production in CAPD: identifying noncompliance
K D Nolph1, Z J Twardowski, R Khanna
1Division of Nephrology, University of Missouri Health Sciences Center, Columbia 65212, USA.
Objective:
To evaluate the ratio of measured creatinine (Cr) production to predicted creatinine production as an index of noncompliance in patients on continuous ambulatory peritoneal dialysis (CAPD).
Design:
A cross-sectional analysis.
Patients:
One hundred and twenty-one patients on CAPD.
Measurements:
We have calculated Cr production from measured Cr outputs in 24-hour collections of urine and dialysate. Predicted Cr productions were calculated from standard tables. Weekly KT/V urea and weekly Cr clearances were determined from the same 24-hour urine and dialysate collections. Lean body mass (LBM) was calculated from the Cr production. Serum albumin concentration was measured.
Results:
The ratio of measured/predicted Cr production correlated positively and significantly with weekly KT/V urea, the protein equivalent of nitrogen appearance (PNA), weekly Cr clearance, and LBM. There was a decline in serum albumin concentration at ratios greater than 1.24, supporting the opinions of previous authors who have suggested that ratios greater than 1.24 are highly suggestive of noncompliance with the dialysis prescription. Defining noncompliance as a ratio greater than 1.24 implied that at least 5% of the female and 17% of the male patients were noncompliant.
Conclusions:
Declining serum albumin concentrations at higher ratios of measured/predicted Cr production support the opinion that this is an index of noncompliance. However, not all noncompliant patients necessarily have a ratio greater than 1.24. Weekly KT/V urea, weekly Ccr and LBM are all artifactually increased by "washout effects" if all exchanges are done only or mainly on the collection day.