Testing for plasma ammonia levels
As soon as hyperammonemia is suspected, plasma ammonia levels should be tested.3,7
Normal levels, according to the Association of Clinical Biochemistry, are:10
- 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 acute hyperammonemia in patients with NAGS deﬁciency
In a hyperammonemic crisis, emergency management procedures should be followed:12
- Contact a physician and medical team experienced in metabolic disorders for instructions, and arrange for emergency transport, if needed.
- Initiate CARBAGLU treatment as soon as the diagnosis of NAGS deﬁciency is suspected, which may be as soon as at birth.
- Administer CARBAGLU with other ammonia lowering therapies, such as alternate pathway medications, hemodialysis, and protein restriction.
For a more comprehensive discussion of emergency management procedures, 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,11 such as NAGS deficiency. Therefore, once elevated plasma ammonia is confirmed, other laboratory investigations that are necessary for differential diagnosis should quickly follow.7,10
These investigations should include:7
- Blood glucose
- Blood gases
- Plasma electrolytes
- Plasma lactate
- Liver Transaminases
- Plasma amino acids
- Blood or plasma acylcarnitines
- Urine amino acids, organic acids, and orotic acid