A seasonal variation in the incidence of neonatal nonhemolytic, unconjugated hyperbilirubinemia has been observed in a small, predominantly agricultural community. A total of 3,096 records, representing all newborns delivered during a 4-year period (1963-1966) in one local hospital and during an overlapping 3-year period (1964-1966) in another, were reviewed. A case was defined as an infant whose highest recorded unconjugated bilirubin level reached 10 mg/100 ml during the first days of life. Infants with clear-cut hemolytic disease of the newborn were excluded from consideration. One hundred seventy cases were identifled. In one hospital, an excess of cases occurred during the fourth quarter of each of the 4 years reviewed. A similar trend was apparent in the second hospital during 2 of the 3 years reviewed.
The cause of this systematic fluctuation is unclear. Insofar as possible, factors commonly associated with neonatal hyperbilirubinemia were excluded. During the peak incidence penods, a surplus of cases among infants fed with tap water-containing formula was noted.
The Spectrum of Hemolytic Disease of the Newborn: Evaluating the Etiology of Unconjugated Hyperbilirubinemia Among Neonates Pertinent to Immunohematological Workup
