April 2026, v.1.2
Updated: April 2026
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- Overview
- Methodology
- Background
- Biochemical Pathway and Nutrition Treatment Rationale
- Nutrition Assessment
- Comparative Standards
- Nutrition Problem Identification
- Nutrition Intervention
- Nutrition Recommendations
- Monitoring and Evaluation
- Resources
- Benefits and Harms of Implementing the Recommendations
- Barriers to Implementation
- Areas for Future Research
- List of Tables
-
Literature Evidence Summary Tables
- T.1 Total Protein and Energy Recommendations for Individuals with Urea Cycle Disorders When Well
- T.2 Monitoring the Nutritional Management of an Individual with UCD when Well
- T.3 Genetic Basis of Urea Cycle Disorders and Related Disorders
- T.4 Nutrition Problem Identification for UCDs
- References
- Contributors
- Appendix A: Recommendation Rating Definitions
- Appendix B: Terms
- Disclaimer
Derived from evidence and consensus based clinical practice
Liver transplantation is a well-supported treatment for many individuals with UCDs, with retrospective cohort studies reporting one- and five-year survival rates exceeding 90% across age groups and UCD diagnoses. The procedure reduces the risk of metabolic decompensation and has been associated with normalization of diet, discontinuation of nitrogen scavenger therapy, and improved cognitive outcomes.
While published data describing formal nutrition assessment during pre-transplant evaluation are limited, clinical consensus supports preoperative nutritional assessment.
Perioperative management strategies to prevent catabolism and hyperammonemia include providing continuous intravenous dextrose (with or without intravenous lipid emulsion), administering nitrogen scavengers and intravenous L-arginine as indicated, and closely monitoring ammonia and plasma amino acids before and after surgery. Postoperatively, IV amino acids are recommended until enteral nutrition is tolerated. Clinical consensus emphasized minimizing fasting duration, ensuring energy provision, and initiating parenteral amino acids if fasting exceeds 24 hours.
Evidence regarding post-transplant L-arginine or L-citrulline supplementation is mixed. While some individuals exhibit persistently low plasma concentrations and receive supplementation based on biochemical findings, recent registry-based analyses have not demonstrated clear long-term clinical or biochemical benefit from routine supplementation, highlighting the need for individualized decision-making guided by laboratory monitoring.
Following transplantation, individuals successfully transitioned to an unrestricted diet, as consistently reported across UCD subtypes. Although nutrition counseling was not explicitly described in published studies, clinical consensus strongly supports individualized counseling to support this transition, address longstanding feeding behaviors, and ensure nutritional adequacy.
Liver Transplantation as a Treatment Modality
1. Consider liver transplantation as an effective and evidence-based treatment option for eligible individuals with a UCD to improve survival and allow for an unrestricted protein diet.
| Insufficient Evidence | Consensus | Weak | Fair | Strong |
| Conditional | Imperative |
Pre-Transplant
1. Perform a comprehensive nutrition assessment during pre-transplant evaluation, including dietary history, anthropometric data, and nutrition-focused laboratory assessments, conducted by a metabolic and/or transplant dietitian.
| Insufficient Evidence | Consensus | Weak | Fair | Strong |
| Conditional | Imperative |
Perioperative Nutrition Support
1. Obtain ammonia and/or plasma amino acids prior to surgery to establish a baseline profile.
2. Minimize fasting (i.e., NPO period) to the shortest duration for surgical safety, and administer continuous IV dextrose at an age-appropriate glucose infusion rate, maintained throughout the procedure to prevent catabolism and hyperammonemia. (Recommendation 2.6.2)
3. Coordinate nutrition care to align with physician-directed use of nitrogen scavengers and/or IV L-arginine hydrochloride administered before and during surgery to support nitrogen clearance and prevent hyperammonemia.
4. If fasting exceeds 24 hours during the perioperative period, provide parenteral amino acids per patient tolerance.
5. Consider monitoring blood ammonia for at least the first 24 hours after transplant to ensure it is safe to initiate an unrestricted protein diet.
6. Use standard post-transplant protein goals to support wound healing (e.g., 2-3 g/kg/day for ages 0-2 years, 1.5-2.0 g/kg/day for ages 2-13 years, and 1.5 g/kg/day for ages 13-18 years or per institutional guidelines).
| Insufficient Evidence | Consensus | Weak | Fair | Strong |
| Conditional | Imperative |
Post-Transplant Amino Acid Supplementation
1. For individuals with CPS or OTC who exhibit low plasma arginine or episodes of hyperammonemia post-transplantation, consider supplementation with L-citrulline guided by plasma arginine concentrations.
2. For individuals with CIT-I or ASA who exhibit low plasma arginine or episodes of hyperammonemia post-transplantation, consider supplementation with L-arginine.
3. Monitor plasma amino acids at least annually in individuals receiving L-citrulline or L-arginine supplementation post-transplant to guide continued use and adjust dosing.
| Insufficient Evidence | Consensus | Weak | Fair | Strong |
| Conditional | Imperative |
Post-Transplant Nutrition Counseling and Diet Liberalization
1. Provide individualized nutrition counseling by a metabolic dietitian, along with ongoing plasma amino acid monitoring, for approximately one year after transplant to support a safe transition to an unrestricted protein diet and ensure continued nutritional adequacy.
2. Maintain long-term monitoring by a metabolic and/or transplant dietitian to evaluate growth, health maintenance, and nutritional status.
| Insufficient Evidence | Consensus | Weak | Fair | Strong |
| Conditional | Imperative |