Can Ammonia Levels Be Elevated in Hemodialysis Patients?
Yes, ammonia levels can paradoxically rise during hemodialysis in a significant proportion of patients, occurring in approximately 43% of hemodialysis patients despite effective urea removal. 1
Understanding the Paradox
While hemodialysis effectively removes urea and is used therapeutically to treat severe hyperammonemia, the dialysis procedure itself can cause a modest but significant rise in blood ammonia levels in certain patients. This counterintuitive finding contrasts with the well-documented reduction in breath ammonia following hemodialysis.
Key Mechanisms
The rise in blood ammonia during hemodialysis correlates with:
- Bicarbonate changes: Strong correlation (r = 0.61, P < 0.01) between rising blood ammonia and increasing serum bicarbonate levels 1
- Hemodynamic instability: In patients who develop elevated ammonia, there is a strong correlation with drops in mean arterial pressure (r = 0.88, P < 0.01) 1
- Intradialytic hypotension: Patients with rising ammonia tend to have lower nadir systolic blood pressures during dialysis (124 ± 8 vs. 136 ± 6 mmHg) 1
Baseline Ammonia Levels
Importantly, baseline blood ammonia levels in hemodialysis patients (before dialysis) are not significantly different from healthy controls or peritoneal dialysis patients. 1 This means chronic kidney disease itself does not inherently cause hyperammonemia, but the dialysis procedure can trigger it.
Clinical Implications
When to Monitor
Monitor ammonia levels in hemodialysis patients who develop:
- Altered mental status during or after dialysis
- Unexplained encephalopathy
- Intradialytic hypotension
- Significant bicarbonate shifts
Special Populations at Risk
Hemodialysis patients with underlying metabolic disorders (such as adult-onset type II citrullinemia) can develop severe hyperammonemia requiring intensified dialysis strategies. In documented cases, increasing dialysis frequency to four 5-hour sessions per week successfully reversed both clinical manifestations and brain MRI abnormalities. 2
Therapeutic Considerations
When hemodialysis is used to treat hyperammonemia (not cause it), ammonia clearance is highly effective:
- Ammonia extraction can exceed 80% with optimized dialysate flow rates 3
- Clearance is blood flow-dependent and influenced by dialysate flow rate and dialyzer surface 3
- Plasma ammonia can decline by 56% within 90 minutes of treatment 4
Dialysis Modality Selection
For treating severe hyperammonemia:
- High-dose continuous venovenous hemodialysis (CVVHD) is recommended as first-line when hemodynamic stability allows 5
- Intermittent hemodialysis provides faster ammonia reduction (50% reduction in 1-2 hours) but carries higher risk of rebound hyperammonemia 5
- Dual dialysis approach (combining intermittent HD with CVVHD) can be effective in critically ill patients 6
Common Pitfalls
- Assuming dialysis always lowers ammonia: Nearly half of patients may experience paradoxical rises
- Overlooking hemodynamic factors: Intradialytic hypotension may trigger ammonia elevation
- Missing metabolic disorders: Underlying urea cycle defects can be unmasked or worsened by standard hemodialysis
- Inadequate monitoring: Ammonia levels should be checked if neurological symptoms develop during or after dialysis
The relationship between hemodialysis and ammonia is bidirectional: while dialysis effectively treats hyperammonemia when used therapeutically, the procedure itself can paradoxically elevate ammonia levels in a substantial minority of patients, particularly those experiencing hemodynamic instability or significant acid-base shifts.