Pediatric emergency medicine trisk 2436 2436

organic acids,
neurotransmitters,
folate, pterins, other
disease-specific
metabolites

Mitochondrial disorders
Nonketotic hyperglycinemia
Neurotransmitter disorders

a Within

disease categories, not all diseases have the laboratory abnormality. In disorders of protein metabolism, carbohydrate metabolism,
and fatty acid oxidation defects and abnormality may be present only during acute crisis.
b Samples, quantities required, collection method, preparation, and storage are institution dependent. Tandem mass spectrometry measures
amino acids and acylcarnitines, derived from carnitine, which combines with acyl-CoA derived from fatty acids and organic acids (which
may have been derived from amino acids). Tandem mass spectrometry may be used as a screen for aminoacidopathies, organic acidemias,
and fatty acid oxidation defects. Confirmation of diagnosis usually requires further testing, including plasma amino acids, urinary organic
acids, histologic examination, DNA analysis, and enzyme and/or biochemical assays.
c Total minimum is 4 mL for organic acids and acylglycines.
EDTA, ethylenediaminetetraacetic acid; GI, gastrointestinal; IEM, inborn error of metabolism.

Hyperammonemia. Ammonia is an intermediary in the catabolism of nitrogen-containing compounds,
particularly amino acids. Normal ammonia levels are less than 100 μg/dL in neonates and less than 80
μg/dL beyond the neonatal period. Elevated ammonia is neurotoxic and immediate treatment should
begin pending confirmation of a specific diagnosis. Early manifestations of hyperammonemia are
anorexia and irritability, followed by rapid progression to vomiting, lethargy, seizures, coma, and death in
hours. Marked hyperammonemia causes brainstem dysfunction leading to deep rapid breathing and
resulting in respiratory alkalosis, a hallmark of urea cycle disorders. Cerebral edema and intracranial
hemorrhage are also common. Children and adolescents may report headache, abdominal pain, and
fatigue. Some patients with chronic hyperammonemia adapt to their elevated ammonia level and may

appear to have no overt symptoms despite elevated ammonia.