What are the best laboratory tests to evaluate the condition of patients undergoing dialysis?

Laboratory Evaluation of Dialysis Patients

For routine monitoring of dialysis patients, prioritize monthly measurement of predialysis hemoglobin, Kt/V or URR for dialysis adequacy, and iron studies (serum ferritin and transferrin saturation), along with monthly electrolytes and quarterly albumin to assess nutritional status and cardiovascular risk.

Core Monthly Laboratory Tests

Dialysis Adequacy Monitoring

• Measure Kt/V or urea reduction ratio (URR) monthly to ensure adequate solute clearance, with target Kt/V ≥1.2 for hemodialysis patients 1
• Obtain predialysis and postdialysis blood urea nitrogen (BUN) samples to calculate these parameters 1
• For hemodialysis patients, draw blood samples before the midweek dialysis session (not after the 3-day interval) to minimize variability 1
• Sample timing is critical: predialysis samples must be drawn before dialysis initiation or immediately upon starting, never after saline infusion 1

Anemia Assessment

• Measure hemoglobin (Hgb) monthly using predialysis samples rather than hematocrit, as Hgb is more stable and accurate 1
• Initiate anemia workup when Hgb falls below 11 g/dL in premenopausal females/prepubertal patients or below 12 g/dL in adult males/postmenopausal females 1
• Hemoglobin is superior to hematocrit because it remains stable at room temperature for 24+ hours, whereas hematocrit falsely elevates by 2-4% with storage due to MCV changes 1

Iron Status Monitoring

• Check serum ferritin and transferrin saturation monthly to guide iron therapy 1
• Target transferrin saturation ≥20% and serum ferritin >100 ng/mL to ensure adequate iron availability for erythropoiesis 1, 2
• Transferrin saturation is more reliable than ferritin alone in dialysis patients because ferritin acts as an acute-phase reactant and may be falsely elevated by inflammation 1
• Consider measuring C-reactive protein when ferritin is elevated to assess whether inflammation is contributing 1

Electrolyte Monitoring

• Measure sodium, potassium, calcium, phosphorus, magnesium, and bicarbonate monthly 1, 3
• Predialysis potassium and calcium levels are particularly important given the dysrhythmogenic risk from electrolyte fluctuations 1, 4
• Be aware that 40% of patients have hypokalemia and 67% have hypophosphatemia immediately post-dialysis 3
• Check magnesium levels routinely, as hypomagnesemia occurs in 60-65% of dialysis patients and causes refractory hypokalemia/hypocalcemia that cannot be corrected without magnesium replacement 4

Quarterly Laboratory Tests

Nutritional and Metabolic Assessment

• Measure serum albumin every 3 months as a marker of nutritional status and predictor of mortality 1, 2
• Albumin levels are significantly associated with hematocrit and overall outcomes 2

Baseline and Periodic Cardiac Evaluation

At Dialysis Initiation

• Obtain baseline electrocardiogram (ECG) and echocardiogram within 1-3 months after achieving dry weight 1
• These tests assess for coronary artery disease, left ventricular hypertrophy (present in 75-80% of dialysis patients), and systolic/diastolic dysfunction 1

Ongoing Cardiac Monitoring

• Perform annual ECGs after dialysis initiation 1
• Repeat echocardiography every 3 years or when clinical status changes (recurrent hypotension, heart failure symptoms, inability to achieve dry weight) 1

Critical Pitfalls to Avoid

Sampling Errors

• Never draw postdialysis BUN samples after blood reinfusion—this falsely elevates the result and underestimates dialysis adequacy 1
• Do not use saline-filled needles for predialysis BUN sampling 1
• Avoid using hematocrit in hyperglycemic patients, as elevated glucose falsely increases MCV and calculated hematocrit 1

Iron Management Errors

• Do not treat hypokalemia or hypocalcemia without first checking and correcting magnesium—these electrolyte abnormalities will be refractory to replacement if magnesium is low 4
• Do not rely on ferritin alone in dialysis patients; always interpret it alongside transferrin saturation and consider inflammatory markers 1
• Only 53% of patients with transferrin saturation <20% and ferritin <800 ng/mL receive appropriate intravenous iron therapy—this represents a major treatment gap 2

Timing and Interpretation Errors

• Do not assume postdialysis electrolytes are stable—fluctuations continue for 4-5 hours after treatment 4
• Avoid drawing labs during the 3-day interdialytic interval, as this introduces greater variability 1
• Do not use automated cell counter results for hematocrit if samples have been stored >8 hours at room temperature or >24 hours refrigerated 1

Special Circumstances

Peritoneal Dialysis Patients

• Establish baseline peritoneal membrane transport characteristics 4-8 weeks after starting daily peritoneal dialysis 1
• Repeat peritoneal equilibration test (PET) or standard peritoneal permeability analysis when clinically indicated, but only when patient is stable and ≥1 month after peritonitis resolution 1

Transplant Candidates

• Patients on the transplant waitlist require additional cardiovascular screening with stress imaging at intervals determined by diabetes status and cardiac risk factors 1

Residual Renal Function

• In patients with residual kidney function, consider using N-acetylcysteine and iso-osmolar contrast (iodixanol) for nephroprotection during angiographic procedures 1