Exploring the reverse J-shaped curve between urea reduction ratio and mortality

Area of Science:

• Nephrology
• Clinical Nutrition
• Biostatistics

Background:

• Dialysis adequacy measures like Kt/V and urea reduction ratio (URR) do not consistently predict survival in hemodialysis patients.
• High Kt/V or URR may be influenced by low urea distribution volume (V), potentially reflecting poor nutritional status.
• Malnutrition could confound the interpretation of URR and Kt/V as indicators of dialysis effectiveness and patient outcomes.

Purpose of the Study:

• To investigate the relationship between dialysis dose metrics (URR, Kt/V) and patient survival.
• To explore the role of nutritional status, specifically urea distribution volume (V), in the observed dose-mortality relationship.
• To determine if high URR or Kt/V values are associated with improved survival or masked malnutrition.

Main Methods:

• Analyzed data from 3,009 hemodialysis patients who underwent bioelectrical impedance analysis.
• Stratified patients into quintiles based on URR and compared nutritional parameters (phase angle, total body water) across quintiles.
• Examined the relationship between dialysis dose (URR, Kt/V, Kt) and mortality, adjusting for the influence of V.

Main Results:

• Significant differences in nutritional status were observed across URR quintiles, with the highest quintile showing more severe malnutrition.
• The relationship between URR and mortality was curvilinear (reverse J-shaped).
• No increased mortality risk was associated with high Kt (clearance x time); higher Kt correlated with better nutritional status.

Conclusions:

• Increased mortality in patients with very high URR or Kt/V may be due to the detrimental effects of underlying malnutrition (reduced V).
• Extremely high URR (>75%) or Kt/V (>1.6) warrants a thorough nutritional status assessment.
• Protein-calorie malnutrition can confound the use of URR and Kt/V as population-level measures of dialysis adequacy.