Measurement of solute clearance in continuous peritoneal dialysis: Kt/V and creatinine clearance
- John M Burkart, MD
John M Burkart, MD
- Section Editor — Dialysis
- Professor of Medicine/Nephrology
- Wake Forest University Medical Center
Dialysis adequacy is an important issue for patients treated with maintenance hemodialysis or peritoneal dialysis. The minimum effective dialysis dose is typically determined by measuring small solute clearance. Common methods used to measure small solute clearance include urea clearance normalized to total body water (Kt/Vurea) and the peritoneal creatinine clearance (CCr) normalized to body surface area (BSA). Both Kt/V and CCr utilize clearance of a surrogate solute (ie, urea or creatinine, respectively) to estimate overall small solute clearance.
The weekly Kt/Vurea is now the preferred method for measuring small solute clearance [1-3]. However, the CCr may still be used in some areas. Although the Kt/V and peritoneal CCr usually correlate, they are occasionally discrepant [4-6].
This topic reviews methods of measuring solute clearance in peritoneal dialysis, including the Kt/V and the CCr.
An overview of prescribing an adequate amount of peritoneal dialysis and the mechanism of solute clearance by peritoneal dialysis are discussed elsewhere. (See "Prescribing and assessing adequate peritoneal dialysis" and "Mechanisms of solute clearance and ultrafiltration in peritoneal dialysis".)
DEFINITIONS AND CALCULATION
The daily Kt/Vurea is calculated from the daily urea clearance (Kt), which is the sum of the product of all drain volumes (peritoneal and residual kidney) and the ratio of the urea concentration in the pooled, drained dialysate or urine to that in the plasma (D/P urea). Kt is normalized to total body water, which is the volume of distribution of urea (V). V may be estimated from published formulas such as the Watson formula . In general, V is approximately equal to 60 percent of ideal body weight for men and 55 percent ideal body weight for women. In practice, most centers use a kinetic modeling program to determine V and Kt/V, although the Kt/V may be manually calculated from the serum urea, pooled dialysate urea, total drain volume, and estimated V. (See "Prescribing and assessing adequate peritoneal dialysis".)
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