Laboratory Diagnostic Tests
Newborn Infants
If a UCD is suspected in a sick neonate, always start treatment before a diagnosis
is confirmed. Neonates with symptomatic hyperammonemia should be transferred
immediately to a medical institution with a neonatal intensive care unit and
pediatric hemodialysis facilities.
Management of hyperammonemia in the neonate requires the following:
Recognition of the disorder
Diagnosis is difficult and delay may hinder successful treatment. Early recognition
allows the organization of the necessary transport and supportive care.
| Laboratory Indications of Urea Cycle Disorder | |
|---|---|
| Test | Result |
| Ammonia | >150 µmol/L |
| Anion gap | <20 |
| Blood glucose | Normal |
| Keytones | Low |
A urea cycle disorder should be considered in all patients who present with symptoms of encephalopathy — irritability, stupor, hallucinations, delusions, and coma. Newborns with urea cycle disorders generally have vomiting, refusal to feed, loss of muscle tone, stupor, and coma.
The following tests should be ordered:15
Ammonia level
pH and CO2
Anion gap
Glucose level
Urine organic acids and orotic acids
Specific enzymes or DNA analysis
A plasma ammonia level greater than 150 µmol/L, a normal anion gap, and a normal glucose level are strongly suggestive of a urea cycle disorder. Amino acid analysis will tentatively identify the specific disorder. DNA analysis is needed for a conclusive diagnosis.
References:
12. Bachman, Claude, and Colombo, J.P. “Diagnostic value or orotic acid excretion in heritable disorders of the urea cycle and in hyperammonemia due to organic aciduria”
European Journal of Pediatrics, 1980, Vol. 134, p.109-113
13.
Tuchman, Mendel, MD and Batshaw, Mark, MD “Management of inherited disorders of ureagenesis”, The Endocrinologist, 2002, Vol. 12, p. 99-109.
14.
Steiner, Robert, MD and Cederbaum, Stephen, MD “Laboratory evaluation of urea cycle disorders” Journal of Pediatrics, 2001,Vol. 128, No. 1, p. S21-29.
15. Summar, Marshall, MD and Tuchman, Mendel, MD, “Proceedings of a consensus conference for the managaement of patients with urea cycle disorders” Journal of Pediatrics, Vol. 128, No. 1, p. S6-10.