• ABO system
  • ABO hemolytic disease of the newborn can range from mild to severe, but generally it is a mild disease.
    • Anti-A antibodies
    • Anti-B antibodies

• Rhesus system (the Rh d antigen and Rh d antibodies do not exist)
  • Rhesus D hemolytic disease of the newborn (often called Rh disease) is the most common form of severe HDN. The disease varies from mild to severe.
  • Rhesus E hemolytic disease of the newborn is a mild condition
  • Rhesus c hemolytic disease of the newborn can range from a mild to severe disease – is the third most common form of severe HDN
  • Rhesus e hemolytic disease of the newborn – rare
  • Rhesus C hemolytic disease of the newborn – rare
  • Antibody combinations (ie anti-Rhc and anti-RhE antibodies occurring together) – can be severe

• Kell system
  • Anti-Kell hemolytic disease of the newborn
    • Anti-K ₁ antibodies – disease ranges from mild to severe – over half of the cases are caused by multiple blood transfusions – is the second most common form of severe HDN
    • Anti-K ₂ ,anti-K ₃ and anti-K ₄ antibodies – rare

• Other blood group antibodies (Kidd, Lewis, Duffy, MN, P and others).

The diagnosis of HDN is based on history and laboratory findings:

• Biochemistry tests for jaundice
• Peripheral blood morphology shows increased reticulocytes. Erythroblasts (also known as nucleated red blood cells) occur in moderate and severe disease.

• Positive direct Coombs test (might be negative after fetal interuterine blood transfusion)

• Positive indirect Coombs test