Diagnosis of ABO HDFN is supported by these findings:
- ABO incompatibility between mother and child, with mother typically group O
- Negative maternal antibody screen
- Weakly positive or negative cord DAT
- Newborn hyperbilirubinemia with jaundice occurring in the first 24 hours
- Increased spherocytes and reticulocytosis in the newborn
- Presence of IgG anti-A or anti-B in cord plasma/serum