How often should lab tests be performed on patients undergoing Continuous Renal Replacement Therapy (CRRT) and what tests are recommended?

Laboratory Monitoring for Patients on Continuous Renal Replacement Therapy (CRRT)

For patients on CRRT, laboratory tests should be performed daily for electrolytes, complete metabolic panel, and coagulation profiles, with more frequent monitoring (every 6-8 hours) during the initial phase or when clinically indicated. 1

Essential Laboratory Tests for CRRT Patients

Daily Monitoring

• Complete blood count (CBC) should be monitored daily to assess for anemia, thrombocytopenia, and other hematologic abnormalities 1
• Complete metabolic panel (including magnesium and phosphorus) should be checked daily to monitor electrolyte balance and acid-base status 1
• Coagulation profiles should be assessed daily, especially if anticoagulation is being used for the circuit 1
• Serum creatinine and BUN should be monitored daily to assess kidney function and adequacy of therapy 1

More Frequent Monitoring (Every 6-8 hours)

• Electrolytes (particularly potassium, calcium, phosphate, and magnesium) should be checked every 6-8 hours during the initial phase of CRRT due to the high risk of electrolyte disturbances 1, 2
• Acid-base status should be monitored every 6-8 hours initially, as metabolic alkalosis or acidosis can develop rapidly 3
• Ionized calcium should be monitored every 6 hours if regional citrate anticoagulation is being used 3

Additional Monitoring

• C-reactive protein (CRP) and serum ferritin should be monitored at least 3 times per week in patients receiving CAR T-cell therapy who are on CRRT 1
• Trace elements (particularly selenium, zinc, and copper) should be monitored regularly as they can be depleted during CRRT due to increased effluent losses 1
• Water-soluble vitamins (especially vitamin C, folate, and thiamine) should be monitored and supplemented due to significant losses in the effluent 1

Monitoring Schedule Based on Clinical Status

Initial Phase (First 24-48 hours)

• Electrolytes, BUN, creatinine, and acid-base parameters should be checked every 6-8 hours 1, 2
• Adjust frequency based on the stability of the patient and previous laboratory results 2

Stabilization Phase

• Once stabilized, laboratory monitoring can be reduced to every 12 hours 2
• After 2-3 days of stability, daily monitoring may be sufficient for most parameters 1

Special Considerations

• Patients with high-intensity CRRT (>35 mL/kg/hr) require more frequent monitoring due to increased risk of electrolyte abnormalities 2, 3
• Patients receiving regional citrate anticoagulation need more frequent monitoring of calcium levels and acid-base status 3
• Patients with large effluent losses should have more frequent monitoring of phosphate levels due to risk of hypophosphatemia 1

Common Pitfalls and Complications

• Hypophosphatemia occurs in 60-80% of ICU patients on CRRT and requires close monitoring and supplementation 1
• Hypokalemia and hypomagnesemia are common during intensive/prolonged CRRT and can lead to cardiac arrhythmias if not promptly corrected 1
• Metabolic alkalosis is more common with citrate anticoagulation (32.5%) compared to heparin (16.2%) or no anticoagulation (13.5%) 3
• Trace element deficiencies can develop over time and may not be apparent without specific monitoring 1

Remember that laboratory monitoring should be tailored to the individual patient's clinical status, the specific CRRT modality being used, and the anticoagulation strategy employed. Prompt recognition and correction of electrolyte and acid-base disturbances are essential to prevent complications during CRRT.