Do patients on dialysis produce urine?

Urine Production in Dialysis Patients

Yes, many dialysis patients continue to produce urine, especially in the early stages of dialysis therapy, though this residual kidney function tends to decline over time. 1

Residual Kidney Function (RKF) in Dialysis Patients

• When hemodialysis therapy is first initiated, most patients have small but significant levels of residual kidney function, and many have normal or even high rates of urine output 1
• This residual kidney function may persist for many months or years, adding continuous solute clearance to the intermittent clearances provided by dialysis treatments 1
• The presence of RKF is one of the most important predictors of a patient's survival in dialysis 1

Importance of Residual Kidney Function

• RKF contributes substantially to solute clearance in dialysis patients 2
• The volume of urine produced allows for more fluid intake, reducing the otherwise larger fluctuations in body fluid volumes between dialysis treatments 1
• RKF helps prevent volume overload syndromes, hypertension, and cardiac hypertrophy 1
• Preservation of RKF is associated with lower mortality risk in hemodialysis patients (odds ratio for death: 0.44) 3
• Patients with urine output at one year after starting hemodialysis have lower all-cause mortality (HR: 0.70) compared to those without urine output 4

Benefits of Preserved Urine Output in Dialysis Patients

• Better quality of life 4
• Lower levels of inflammation markers (C-reactive protein and interleukin-6) 4
• Reduced erythropoietin requirements (approximately 12,000 U/week lower in those with urine output) 4
• Better volume control 5
• Enhanced clearance of protein-bound and middle molecules 5

Monitoring Residual Kidney Function

• RKF should be monitored routinely in hemodialysis patients 4
• For patients with significant RKF whose dialysis prescription has been modified based on this function, urine volume should be measured monthly 1
• In peritoneal dialysis patients, a daily creatinine excretion in urine and dialysate that differs from baseline by more than 15% should prompt investigation 6
• The average of renal creatinine and urea clearance provides a superior estimate of RKF in dialysis patients compared to daily urine volume alone 5

Decline of Residual Kidney Function

• RKF is subject to temporary or permanent reduction caused by numerous toxic insults that often confront patients with end-stage renal disease 1
• Historically, RKF decreased more rapidly in patients initially treated with hemodialysis compared to peritoneal dialysis 1
• Recent studies show that RKF is preserved better in hemodialysis patients than in the past, possibly due to:
  • Use of more biocompatible membranes
  • Discontinuation of acetate as a bicarbonate precursor
  • High-flux dialysis
  • Earlier initiation of dialysis therapy, especially in patients with diabetes 1
• With the use of ultrapure water to dilute concentrated dialysate, RKF may decrease at a rate similar to that in peritoneal dialysis patients 1

Clinical Implications

• Striving to preserve RKF in hemodialysis patients is recommended as a clinical practice guideline (Evidence Level A) 1
• Methods for preserving RKF differ among patients (Evidence Level B) 1
• The development of methods to assess and preserve RKF is important and may improve dialysis care 4
• Newer methods to estimate RKF without urine collection using serum biomarkers like β-trace protein and β2-microglobulin are being developed 2, 7

In summary, while many dialysis patients do produce urine, especially when first starting dialysis, this function tends to decline over time. Preserving this residual kidney function is associated with significant survival benefits and should be a priority in the clinical management of dialysis patients.