The purpose of this study is to compare the demographic, metabolic, and genomic characteristics of patients who develop severe hyperbilirubinemia (serum bilirubin level in the "high risk zone of greater than the 95th percentile based on the Bhutani nomogram) to patients who never developed significant hyperbilirubinemia (bilirubin level in "low risk zone of less than the 40th percentile" on Bhutani nomogram and who did not require any treatment for hyperbilirubinemia). Our primary goal is to determine if common gene mutations occur at a greater frequency in patients with severe hyperbilirubinemia than in neonates without significant hyperbilirubinemia.