Testing for plasma ammonia levels
As soon as hyperammonemia is suspected, plasma ammonia levels should be tested.1,4
Normal levels, according to the Association of Clinical Biochemistry, are:8
- Premature neonates: < 150 μmol/L
- Term neonates: < 100 μmol/L
- Infants: < 40 μmol/L
- Adults: 11-32 μmol/L
- Proper procedures for obtaining plasma ammonia levels must be followed in order to prevent measurement errors, including false high ammonia levels.
- Low or slightly elevated ammonia levels should lead to retesting, particularly since ammonia concentrations can fluctuate and may not entirely correlate with already impaired brain function.
- Management should be guided by the clinical condition of the patient, rather than solely ammonia concentrations.
Emergency management for hyperammonemic crisis
In a hyperammonemic crisis, emergency management procedures should be followed:
- Administration of fluids, dextrose, and interlipids to mitigate catabolism and typical dehydration.
- Administration of antibiotics plus a sepsis workup to treat potential triggering events or primary sepsis.
- Complete protein restriction is recommended to be maintained for 12 to 36 hours.
- Please see section 5.1 of the Full Prescribing Information.
For the complete list refer to the Urea Cycle Disorders Consortium.
Get instructions for 24/7 STAT delivery of CARBAGLU® (carglumic acid) for hospital emergencies
Additional biochemical investigations
The causes of hyperammonemia are diverse and include liver failure, infection, medications, and inborn errors of metabolism,9 such as NAGS deficiency. Therefore, once elevated plasma ammonia is confirmed, other laboratory investigations that are necessary for differential diagnosis should quickly follow.
These investigations should include:1
- Blood glucose
- Blood gases
- Plasma amino acids
- Blood or plasma acylcarnitines
- Urine amino acids, organic acids, and orotic acid