Pediatric emergency medicine trisk 2439 2439

media (do not use culture media if
planning for microscopic studies),
normal saline without preservative, or
normal saline–soaked sterile gauze in
sterile tube, freeze at –70°C
Fibroblast culture provides unlimited
specimen
Organ biopsy
Brain b
Heart muscle b
Liver a 1 cm3 , 10–20
mg, ≤0.5 cm thick
Kidney b

Histochemical light and/or electron Biopsy potentially affected organs,
microscopy
collect within 1–2 hrs after death
Enzyme activity
Biochemical metabolites
Mitochondrial studies

Spleen b
Skeletal muscle 20–50
mg, ≤0.5-cm thick
Bile
Bile 2 mL

Needle or open incisional biopsy, sterile
technique, wrap in aluminum foil, dry
ice, freeze at −70°C, screw-top
airtight vial

Some assays may need to be performed
on fresh specimens

Bile acids
Acylcarnitines

a If

family declines autopsy but gives permission for specimen collection, or if unable to obtain autopsy within hours of death, collect blood,
urine, and CSF; perform punch or open incisional biopsy of skin and needle biopsy of liver and skeletal muscle; take photographs of
dysmorphic features; and obtain radiologic studies to evaluate for neurologic, cardiac, or skeletal abnormalities. Obtain parental permission.
Tests that are not accurate using postmortem specimens are those for serum amino acids, lactate, pyruvate, and total and free carnitine
assessment. Consider developing postmortem specimen collection kit for ED that contains necessary equipment, specimen containers, and
institution-specific instructions.
b Obtain an autopsy if autopsy permission granted.
EDTA, ethylenediaminetetraacetic acid; PCR, polymerase chain reaction; ED, emergency department.

Hyperammonemia is the hallmark of urea cycle defects but also occurs in organic acidemias and fatty
acid oxidation defects as a consequence of secondary inhibition of the urea cycle. Ammonia levels are
typically highest in urea cycle defects and may exceed 1,000 μg/dL. Ammonia levels in organic
acidemias are usually less than 500 μg/dL during decompensation but may exceed 1,000 μg/dL.
Hyperammonemia in fatty acid oxidation defects, if present, is usually less than 250 μg/dL. Transient
hyperammonemia of the newborn should be considered in the differential diagnosis, particularly if
hyperammonemia is present on the first day of life. Hyperammonemia directly stimulates the respiratory
center, resulting in tachypnea. Ammonia level higher than 250 μg/dL with respiratory alkalosis in the
absence of metabolic acidosis is highly suggestive of a urea cycle defect. Proper collection and handling
of blood for ammonia determination is critical to prevent falsely elevated values. Abnormal levels should
be confirmed immediately using proper technique for drawing and handling.
Patients with urea cycle defects may have compensatory metabolic acidosis. Patients with organic
acidemias and fatty acid oxidation defects and hyperammonemia have primary metabolic acidosis usually

without respiratory alkalosis. Patients with hyperammonemia due to organic acidemias usually have
marked ketosis and normal glucose level, whereas those with fatty acid oxidation defects usually have
hypoketotic hypoglycemia. Even during minor illnesses, protein catabolism may result in
hyperammonemia. In patients with hyperammonemia, liver function should be evaluated. Mild elevation
of transaminases may be seen in metabolic disorders in each category. Plasma should be sent for amino