Pediatric emergency medicine trisk 0891 0891
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Bilirubin Measurement. Transcutaneous measurements of bilirubin are
correlated with serum bilirubin; however, they are inaccurate at higher levels
(greater than 12 to 15 mg/dL), and thus are best used as a screen. A TSB should
always be obtained when therapeutic intervention is being considered.
Nearly all published data regarding the correlation of TSB levels to kernicterus
or developmental outcome are based on capillary blood. Data on the relationship
between capillary and venous sampling are conflicting. Capillary sampling is
endorsed by the AAP; a confirmatory venous sample is not required. In neonates,
it may be important to determine the rate of rise of TSB with serial
measurements.
It is imperative to note that many clinical laboratories require the total and
fractionated bilirubin to be ordered separately, as the total bilirubin reported on
the hepatic function or comprehensive metabolic panels is unreliable in infants
under 1 month of age. The ED clinician should be familiar with the accuracy of
his or her laboratory assay in order to minimize error in the evaluation and
management of neonates with suspected hyperbilirubinemia.
Other Laboratory Studies. If the TSB level is below 12 mg/dL, rises slowly,
and resolves before 8 days of age, one can diagnose physiologic
hyperbilirubinemia without further laboratory studies. When these conditions are
not met, further testing is required to determine the etiology of elevated serum
bilirubin.
A complete blood cell count should be obtained to evaluate for anemia. A
peripheral blood smear should be examined microscopically for clues as to the
etiology of the anemia: characteristic abnormal morphology, such as sickle cells,
spherocytes, or elliptocytes, may be identified; helmet and fragmented cells are
diagnostic of a microangiopathic hemolytic anemia; malarial ring forms may be
apparent. The reticulocyte count may be elevated in the setting of hemolysis.
Patients with anemia or hemolysis should also have a Coombs test performed to
look for evidence of autoimmune hemolysis. In patients with a TSB level above
threshold for exchange transfusion, a serum albumin should be obtained, and ratio
of bilirubin to albumin should be calculated. End-tidal carbon monoxide
concentration (ETCOc) provides a noninvasive assessment of bilirubin
production, and may be utilized to aid in confirmation of active hemolysis.
The child with fever, hypothermia, or ill appearance should be evaluated for
serious bacterial infection, including blood, urine, and cerebrospinal fluid cultures
as indicated. Serum electrolytes should be obtained in patients with clinical signs
of dehydration, and those with a history of emesis or excessive stool output.
