Patients with progressive chronic kidney  disease (CKD) often require dialysis when their glomerular filtration rate (GFR) is less than 15 mL/min. The initiation of dialysis does not necessarily cause the natural “native” kidneys to quit working, but their function continues to decline with time. This residual kidney function declines at a faster rate with hemodialysis than with PD. Clinical trials have demonstrated residual kidney function protects the patient from cardiovascular events such as heart attacks. Keeping residual kidney functions for as long as possible may help reduce a patient’s risk for heart attack.

How is residual kidney function measured?
Residual kidney function is ideally measured by a blood test and a 24-hour urine collection – averaging two key values, the 24-hour creatinine clearance (CrCL) and the 24-hour urea clearance. The average of these values (CrCL and urea) are used to calculate the GFR. Urine volume of 100ml
per day or more (approximately three ounces) is considered significant and should be included with the measurement to determine the effectiveness of PD therapy.

GFR can be estimated using mathematical equations. Equations are highly variable once kidneys fail. Therefore, in patients undergoing dialysis, actual measurements are more reliable. The decision on when to begin dialysis in Stage 5 CKD is highly variable, and depends upon many factors, including
the degree of uremia, overall health status, coexisting cardiac condition and fluid management needs. Therefore, patients will start dialysis with varying degrees of residual kidney function. Once dialysis has begun, residual kidney function should be measured along with PD adequacy at one month, and every four months thereafter. When residual urine output is greater than 100mL per day, residual kidney function measurements should be included in the weekly adequacy goal. Residual kidney function, because of its importance in achieving a patient’s adequacy goal, should be assessed at least every two months. The weekly adequacy goal is defined by the term “Kt/V”. “Kt” stands for urea clearance and “V” stands for body. This number is calculated based on the results of multiple tests including blood analysis, urine analysis, PD solution analysis and body weight.