Evaluation and management of increasing blood urea nitrogen (BUN) among end-stage renal disease patients on peritoneal dialysis*

BUN: blood urea nitrogen; PET: peritoneal equilibration test.
*

• The BUN is a marker for solute clearance and is monitored monthly. The BUN increases when total solute clearance decreases. However, the BUN may also go up because of increased production of urea and other solutes due to excessive dietary protein intake, increased catabolism, or because of increased urea absorption in the setting of gastrointestinal bleeding.
• Progressive increases in the BUN should prompt an evaluation for decreased clearance and increased production and/or absorption of urea. This algorithm presents a stepwise approach to the evaluation.
• Kt/Vurea provides a measure of solute clearance by peritoneal dialysis. The Kt/Vurea is calculated from the daily peritoneal urea clearance (Kt), which is the product of the total 24-hour peritoneal drain volume and the ratio of urea concentration in the pooled drained dialysate to plasma. V is the volume of distribution of urea, which is 60% of ideal body weight in men and 55% ideal body weight in women.
• 24-hour urea clearance provides a measure of solute clearance by residual renal function. The 24-hour urea clearance per day is equal to [urine urea (mg/dL) × urine volume (mL)]/plasma urea (mg/dL) × 1440 minutes/day.

¶ The severity of acidosis required to increase catabolic rate is not known. We generally target serum bicarbonate >22 mEq/L.
Δ The PET is a highly reproducible procedure that characterizes solute transport and ultrafiltration across the peritoneal membrane. The PET is used to classify membrane function in order to optimize the dialysis prescription. Since transport characteristics can change over time, the PET is also used as a diagnostic test to identify causes of reduced solute clearance.
◊ Occasionally, a cause for increasing BUN is not found. In such circumstances, it is important to assess the overall patient. If there is no evidence of uremia and declining nutrition and peritoneal dialysis is otherwise going well, many clinicians would just continue peritoneal dialysis as is. Uremia and nutrition are discussed in UpToDate topics on uremic encephalopathy and assessment of nutritional status in hemodialysis.