Pediatric emergency medicine trisk 608

TABLE 95.4
INITIAL LABORATORY STUDIES a


Test
Blood
CBC (plasma)

Laboratory abnormality Indications, comments
metabolic diseases a

Neutropenia (± vacuoles),
anemia, and/or
thrombocytopenia
Organic acidemias
Urea cycle defects
Carbohydrate
intolerance disorders
Carbohydrate
production/utilization
disorders
Lysosomal storage
disorders
Mitochondrial disorders
Glucose (serum)
Hypoglycemia
Aminoacidopathies
Organic acidemias
Fatty acid oxidation
defects
Carbohydrate

intolerance disorders
Carbohydrate
production/utilization
disorders
Mitochondrial disorders
Test of acid–base
Primary metabolic
status (serum)
acidosis
Electrolytes
Aminoacidopathies
Anion gap
Organic acidemias
pH (arterial or
Fatty acid oxidation
venous)
defects
Carbohydrate
intolerance disorders
Carbohydrate
production/utilization
disorders
Mitochondrial disorders
Primary respiratory
alkalosis
Urea cycle defects
Ammonia (plasma) Hyperammonemia
Aminoacidopathies
Organic acidemias
Urea cycle defects

Neutropenia may be masked by infection. Patients with
certain IEMs are at increased risk of infection;
infection can also precipitate metabolic crisis
Anemia hemolytic, megaloblastic, or normocytic,
depending on specific IEM

Hypoglycemia may be due to primary defect of
gluconeogenesis or glucose consumption that
exceeds production

Na+ , K+ , Cl− usually normal unless abnormal
secondary to vomiting, which may produce
hyperchloremic metabolic acidosis, or to
rhabdomyolysis, which may result in hyperkalemia
Normal bicarbonate does not rule out amino or organic
acidemias

Obtain if altered consciousness, persistent or recurrent
unexplained vomiting, recurrent dizziness or ataxia,
primary metabolic acidosis with increased anion gap,


Fatty acid oxidation
defects

primary respiratory alkalosis in the absence of toxic
ingestion
Must be free-flow venous (no tourniquet) or arterial.
Arterial preferred because skeletal muscle releases

ammonia, ice sample immediately, assay promptly
Newborns 90–150 μg/dL, children 40–120 μg/dL,
adults 18–54 μg/dL
(www.pediatriccareonline.org/pco/ub/view/Pediatricdrug-Lookup/153930/0/Normal-Laboratory-Valuesfor-Children )
Normal <100 μg/dL, neonate <80 μg/dL>1 mo
False positives—valproic acid
Obtain if vomiting, jaundice, and/or hepatomegaly
Hyperbilirubinemia predominantly conjugated, except
galactosemia first few days may be unconjugated

Liver function tests Hyperbilirubinemia
(serum)
Aminoacidopathies
Bilirubin
(tyrosinemia)
Transaminases
Carbohydrate
intolerance disorders
Clotting factors
Elevated transaminases
Aminoacidopathies
Organic acidemias
Urea cycle defects
Fatty acid oxidation
defects
Carbohydrate
intolerance disorders
Carbohydrate
production/utilization
disorders

Lysosomal storage
disorders
Mitochondrial disorders
Peroxisomal disorders
Muscle function
Abnormal muscle
Obtain if muscle weakness, tenderness, cramping,
tests (serum)
enzymes
atrophy, exercise intolerance
Lactate
Carbohydrate
Carnitine deficiency due to carnitine transport
dehydrogenase
production/utilization
disorders or secondary to organic acidemias, fatty
disorders
acid oxidation defects
Aldolase
Fatty
acid
oxidation
Creatine kinase
defects
Mitochondrial disorders
Urine
Reducing
substances
(Clinitest)

Aminoacidopathies
(tyrosinemia,
alkaptonuria)
Carbohydrate intolerance
disorders

Clinitest positive for reducing substances and dipstick
negative for glucose (glucose oxidase reaction)
False positives—penicillins, salicylates, ascorbic acid,
drugs excreted as glucuronides


Ketones (Ketostix,
Acetest)

Myoglobin

Absence of reducing substances does not eliminate
possibility of IEM
Elevated ketones
Ketones detected by Ketostix, Chemstix, Acetest
Aminoacidopathies
Inappropriate ketones
Organic acidemias
Ketonuria in neonates
Carbohydrate
Ketonuria, normal glucose beyond neonate
intolerance disorders Low/absent ketones, hypoglycemia beyond neonate
Carbohydrate
production/utilization

disorders
Mitochondrial disorders
Absent ketones,
hypoketosis
Fatty acid oxidation
defects
Myoglobin present
Not always present, even with rhabdomyolysis,
especially if creatinine kinase <10,000 IU
Organic acidemias
Carbohydrate
production/utilization
disorders
Mitochondrial 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.
IEM, inborn error of metabolism.
Adapted from Weiner DL. Inborn errors of metabolism. In: Aghababian RV, ed. Emergency Medicine: The Core Curriculum . Philadelphia,
PA: Lippincott-Raven; 1999:705.

Hypoglycemia. Serum glucose level of less than 40 mg/dL in the neonate and less than 50 mg/dL
beyond the neonatal period should be considered abnormally low. Even with poor oral intake and/or
metabolic stressors, hypoglycemia less than 45 mg/dL is unusual in the normal child. Hypoglycemia may
cause a decreased level of consciousness, irritability, and seizures. Newborns may also have a highpitched cry, hypothermia, cyanosis, and poor feeding. In the older child or adult, symptoms may include
headache, blurred vision, repeated yawning, diaphoresis, pallor, and nervousness. Hypoglycemia most
commonly occurs with fatty acid oxidation defects, disorders of carbohydrate metabolism, and
hyperinsulinemic states. Low serum glucose can also be seen with aminoacidopathies and organic

acidemias due to inhibition of hepatic gluconeogenesis in these disorders. In patients with hypoglycemia,
absence of ketonuria is highly suggestive of a fatty acid oxidation defect. On the other hand, neonates
should never have ketonuria, and when present, it is suggestive of an IEM. Beyond the neonatal period,
hypoglycemia with inappropriately low or absent ketones is also always abnormal. The presence of
urinary ketones in a patient with hypoglycemia does not rule out an IEM, particularly short-chain fatty
acid oxidation defects, organic acidemias, disorders of carbohydrate metabolism, or ketotic hypoglycemia
of childhood. Hypoketosis, if not evident from the urine, can be determined by measuring ketones (3hydroxybutyrate and acetoacetate) and free fatty acids in blood. In patients with hypoglycemia, the
following laboratory studies should be sent: plasma amino acids, acylcarnitine, urine organic acids and
acylglycines, serum cortisol, insulin, liver function tests (LFTs), and ammonia. Growth hormone is not an
informative test in the acute setting. Causes of hypoglycemia other than IEM include liver disease;
hyperinsulinemia; toxic ingestions of salicylates, β-blockers, ethanol, or polyethylene glycol; maternal
diabetes/gestational diabetes; prematurity or small for gestational age; asphyxia; and sepsis.