What is the recommended lab test schedule for a patient with impaired renal function on dialysis?

Laboratory Test Schedule for Patients with Impaired Renal Function on Dialysis

For patients on dialysis, laboratory tests should be performed at least once every 4 months for total solute clearance measurement and every 2 months for residual kidney function assessment if urine output exceeds 100 mL/day. 1

Core Laboratory Monitoring Schedule

For All Dialysis Patients:

• Total solute clearance (Kt/Vurea): Measure within the first month after initiating dialysis and at least once every 4 months thereafter 1
• Peritoneal equilibration test (PET): For peritoneal dialysis patients, perform within the first month and at months 4 and 6 1
• Serum electrolytes: Check every 6-12 months for stage G3 CKD, every 3-5 months for stage G4 CKD, and every 1-3 months for stage G5 CKD 1
• Complete blood count: Perform systematically or according to clinical context to monitor for anemia 1
• Metabolic parameters: Calcium, phosphate, PTH, and vitamin 25(OH)D should be monitored regularly (every 6-12 months for stage G3 CKD, every 3-5 months for stage G4 CKD, and every 1-3 months for stage G5 CKD) 1

For Patients with Residual Kidney Function:

• 24-hour urine collection: Obtain at a minimum of every 2 months if residual kidney volume exceeds 100 mL/day 1
• Residual kidney function: Monitor at least quarterly and as soon as possible after any event that might have acutely reduced residual kidney function 1
• Urine volume and solute clearance: For patients on "incremental" peritoneal dialysis, measure every 2 months; for patients on "full dose" peritoneal dialysis, measure every 4 months 1

Specific Laboratory Tests to Monitor

Nutritional Status Monitoring:

• Serum albumin: Monitor regularly as it correlates with survival in dialysis patients 2
• Serum prealbumin (transthyretin): Consider monitoring as values below 30 mg/dL are associated with increased mortality risk 3, 2
• Normalized protein catabolic rate: Monitor to assess protein intake adequacy 4, 3

Dialysis Adequacy Monitoring:

• Blood urea nitrogen (BUN): Measure pre-treatment and post-treatment levels to calculate Kt/V 1, 5
• Serum creatinine: Monitor regularly as it reflects muscle mass and dialysis adequacy 5, 2
• For peritoneal dialysis patients: Serum samples should be obtained at the midpoint of the daytime empty period for NIPD patients or at the midpoint of daytime dwell(s) for CCPD patients 1

Metabolic Complications Monitoring:

• Liver enzymes, pancreatic enzymes: Monitor according to clinical context 1
• Renal function tests: Monitor systematically or according to clinical context 1
• Metabolic bone disease markers: Calcium, phosphorus, alkaline phosphatase, PTH, and 25-hydroxy-vitamin D 1

Special Considerations

• Timing of blood draws: For hemodialysis patients, blood samples should be drawn pre-dialysis for most tests 1
• Dialysate collection: For peritoneal dialysis adequacy studies, use either the "batch" method (collecting all effluent bags) or the "aliquot" method (taking proportional samples from each bag) 1
• Peritonitis impact: Be aware that peritoneal solute transport increases during peritonitis and may take between 3 days to 1 month to recover, which can affect test results 1

Common Pitfalls to Avoid

• Do not rely solely on estimated GFR: Creatinine-based formulae are inaccurate in ESKD patients and should not be the only factor in clinical decision-making 6
• Do not neglect residual kidney function: Even in chronic hemodialysis patients, preserving residual function has beneficial effects on nutritional parameters 4
• Do not overlook glucose interference: Dialysate creatinine concentration should be corrected for the presence of glucose, which can interfere with some creatinine measurement methodologies 1
• Do not miss compliance issues: Following creatinine appearance in dialysate and urine longitudinally can help evaluate patient compliance with the dialysis prescription 1

By following this laboratory monitoring schedule, clinicians can effectively track dialysis adequacy, nutritional status, and metabolic complications in patients with impaired renal function on dialysis, allowing for timely interventions to improve outcomes.