What toxins can dialysis effectively remove from the blood?

Toxins Effectively Removed by Dialysis

Dialysis effectively removes water-soluble small molecules, certain electrolytes, and some middle molecules, but is limited in clearing protein-bound uremic toxins and larger molecules that contribute significantly to uremic symptoms. 1

Types of Toxins Removed by Dialysis

Effectively Removed Toxins

• Small water-soluble compounds (molecular weight <500 Da):
  • Urea (primary marker used for dialysis adequacy) 1
  • Creatinine 1
  • Electrolytes: potassium, phosphate, sodium 1
  • Uric acid (70-100 mL/min clearance in hemodialysis) 1

Partially Removed Toxins

• Middle molecules (500-60,000 Da):
  • Better removed with high-flux membranes or hemodiafiltration 2
  • Require longer dialysis sessions for effective clearance 1
  • Examples include various peptides and inflammatory mediators 3

Poorly Removed Toxins

• Protein-bound uremic toxins (PBUTs):
  • p-cresol sulfate 4
  • Indoxyl sulfate 4
  • Polyamines 4
  • Current dialytic methods offer limited removal 3
  • These toxins contribute significantly to uremic symptoms despite "adequate" dialysis 2

Dialysis Modalities and Toxin Removal

Hemodialysis

• Primarily removes small water-soluble molecules through diffusion 1
• Urea clearance approximately 70-100 mL/min 1
• Plasma urea levels typically fall by about 50% with each 6-hour treatment 1
• Conventional adequacy metrics (Kt/V) don't reflect clearance of all uremic toxins 2

Peritoneal Dialysis

• Often characterized by better removal of middle molecules compared to conventional hemodialysis 3
• Less efficient for rapid removal of solutes and fluid compared to hemodialysis 1
• Limited usefulness for patients requiring significant solute removal (urea, potassium, phosphate) 1

Continuous Renal Replacement Therapies (CRRT)

• Associated with better hemodynamic stability and fluid overload control 1
• May provide more consistent clearance over time compared to intermittent hemodialysis 1

Clinical Applications and Considerations

Specific Toxin Removal Scenarios

• Lithium poisoning: Hemodialysis is an effective and rapid means of removing lithium in severely toxic patients 5
• Methanol poisoning: Hemodialysis should be considered with significant metabolic acidosis or methanol concentration ≥50 mg/dL 6
• Tumor Lysis Syndrome: Dialysis effectively removes uric acid and phosphate, improving hyperphosphatemia, hyperkalemia, and hypocalcemia 1

Limitations of Current Dialysis Approaches

• Dialysis clearance is only about 10-20% of physiological clearance for index substances like urea or creatinine 1
• Even less effective for higher molecular weight solutes 1
• Beneficial substances (amino acids, water-soluble vitamins) can be lost during dialysis 1
• Conventional dialysis adequacy metrics don't account for protein-bound toxins 4

Future Directions

• Development of membranes capable of removing solutes over an expanded molecular size range 7
• Incorporation of convection with longer and more frequent treatments 7
• Novel approaches to conserve proteins while removing toxins 7
• Potential for microbial-based approaches to metabolize nitrogenous waste products 8

Dialysis prescription should ideally consider both filtration (represented by urea clearance) and secretion (represented by at least one protein-bound toxin) for a more comprehensive assessment of uremic toxin removal 4.