The Bhutani curve11 is a widely used, validated nomogram based on pre-discharge hour-specific serum bilirubin measurements. (Go to http://pediatrics.aappublications.org/content/114/1/297 and see Figure 2.) It is the most reliable way to assess the risk for subsequent development of significant hyperbilirubinemia requiring phototherapy.9 As such, it is the basis for several online calculators and apps such as BiliTool (bilitool.org).
An alternative nomogram developed by Varvarigou et al12 is available for predicting significant hyperbilirubinemia based on transcutaneous bilirubin assessment. (Go to https://pdfs.semanticscholar.org/a9a6/5a988dba7a3442bcebc149ad5aea5e3c35d5.pdf and see Figure 3.) The American Academy of Pediatrics (AAP) supports the use of either bilirubin assessment for the screening and diagnosis of hyperbilirubinemia in infants ≥35 weeks’ gestation.9
Neurotoxicity risk factors. It is important to differentiate the major and minor risk factors for severe hyperbilirubinemia from neurotoxicity risk factors, also listed in TABLE 3.9 Neurotoxicity risk factors are indicative of conditions that may affect albumin binding of bilirubin and are thought to lower the threshold at which bilirubin may cross the blood-brain barrier and render the brain more susceptible to damage from bilirubin. These neurotoxicity risk factors should be applied to the AAP phototherapy nomogram (see Figure 3 at pediatrics.aappublications.org/content/114/1/297) to determine the threshold for initiation of phototherapy in infants with hyperbilirubinemia.9
Few investigators have attempted to define risk factors for the development of poor neurologic outcomes associated with hyperbilirubinemia. Evidence to date has not allowed the determination of a specific bilirubin level at which subsequent development of kernicterus occurs.9 The limited data available suggest a poor correlation between TSB level and bilirubin-induced neurologic dysfunction.13
(For more on kernicterus, as well as ABE and bilirubin-induced neurologic dysfunction [BIND], see “Why do we worry about hyperbilirubinemia?”9,14-16)
SIDEBAR
Why do we worry about hyperbilirubinemia?
When circulating bilirubin crosses the blood-brain barrier, neurologic dysfunction can occur that may become permanent. Bilirubin-induced neurologic dysfunction (BIND) occurs on a spectrum, beginning with acute bilirubin encephalopathy (ABE) and progressing to the irreversible condition—kernicterus.
The incidence of BIND has not been well documented; rates of kernicterus and ABE are thought to be about 1 in 133,000,16 but ABE and kernicterus are not reportable conditions in the United States, so exact prevalence is unknown.
Acute bilirubin encephalopathy may present subtly at first with lethargy, hypotonia, and a high-pitched cry. If not corrected, the condition can progress to hypertonicity (with arching of the neck and trunk), poor sucking, and irritability. It can lead to apnea, intractable seizures, respiratory failure, and even death.14
Kernicterus was originally a term used to describe the yellow bilirubin-staining of brainstem nuclei and the cerebellum seen on autopsy,9 but is now synonymous with chronic bilirubin encephalopathy. Kernicterus describes the irreversible manifestations of bilirubin neurotoxicity that often present as a classical tetrad of motor deficits (athetoid cerebral palsy), auditory processing deficits (with or without hearing loss), oculomotor deficits (especially impairments of upward vertical gaze), and enamel dysplasia of deciduous teeth.15 Abnormal magnetic resonance imaging of the globus pallidus and subthalamic nuclei is often seen in infants with kernicterus.14
Continue to: Diagnosis relies on TSB and/or TcB