title: Isoimmunization is unlikely to be the cause of hemolysis in ABO-incompatible but direct antiglobulin test-negative neonates.
abstract: OBJECTIVE
  It is stated that the direct antiglobulin (Coombs') test (DAT) may be negative in ABO hemolytic disease of the newborn. Thus, significant jaundice in neonates who are A-B incompatible with their mothers but DAT test negative is often attributed to isoimmunization and another diagnosis is not sought. We wished to determine the rate of bilirubin production, as an objective measure of hemolysis, in 2 groups of DAT-negative neonates--ABO-compatible and ABO-incompatible--and in DAT-positive ABO-incompatible neonates.
  
  
  METHODS
  In consecutive, term, healthy newborns who were admitted to the general care nursery, we measured the level in parts per million (ppm) of end-tidal breath carbon monoxide (CO), corrected for inspired CO (ETCOc), an index of the rate of bilirubin production. We compared the levels in DAT-negative ABO-incompatible neonates with those in ABO-compatible neonates and with the levels in DAT-positive ABO-incompatible neonates. Statistical analysis was performed using 2-sample t and chi(2) tests.
  
  
  RESULTS
  There was no significant difference between the mean 12-hour ETCOc levels in DAT-negative ABO-incompatible neonates (n = 60, 2.2 +/- 0.6 ppm) versus DAT-negative ABO-compatible neonates (n = 171, 2.1 +/- 0.6 ppm), although there was a difference between the mean levels in DAT-positive ABO-incompatible neonates (n = 14, 3.4 +/- 1.8 ppm) and the DAT-negative groups. Four DAT-negative ABO-incompatible neonates had elevated ETCOc levels; in 2, we diagnosed a specific hematologic abnormality, namely, glucose-6-phosphate dehydrogenase deficiency in 1 and elliptocytosis in the other.
  
  
  CONCLUSIONS
  In DAT-negative newborns with significant jaundice or increased bilirubin production, even if ABO-incompatible, a cause other than isoimmunization should be sought.
authors.affiliation: Department of Pediatrics, the University of Chicago Pritzker School of Medicine, Chicago, Illinois 60637, USA. mhersche@midway.uchicago.edu
authors.forename: Marguerite
authors.initials: M
authors.lastname: Herschel
authors.forename: Theodore
authors.initials: T
authors.lastname: Karrison
authors.forename: Ming
authors.initials: M
authors.lastname: Wen
authors.forename: Leslie
authors.initials: L
authors.lastname: Caldarelli
authors.forename: Beverly
authors.initials: B
authors.lastname: Baron
mesh_terms: D001663:Bilirubin / Q000096:biosynthesis*; D001944:Breath Tests / Q000379:methods; D002248:Carbon Monoxide / Q000032:analysis; D003298:Coombs Test / Q000706:statistics & numerical data*; D004899:Erythroblastosis, Fetal / Q000175:diagnosis* / Q000209:etiology / Q000276:immunology; D006801:Humans; D007231:Infant, Newborn; D007567:Jaundice, Neonatal / Q000175:diagnosis / Q000276:immunology / Q000378:metabolism; D012203:Rh Isoimmunization / Q000150:complications / Q000175:diagnosis* / Q000276:immunology
chemical_list: D002248:Carbon Monoxide; D001663:Bilirubin