Neonatal Alloimmune Thrombocytopenia

Basics

Basics

Basics

Description

Description

Description

Neonatal alloimmune thrombocytopenia (NAIT) is one of the major causes of severe thrombocytopenia in the newborn.

  • Analogous to ABO/Rh incompatibility but involves platelets instead of RBCs
  • Presents with bleeding complications including petechiae, bruising, mucosal bleeding, and/or intracranial hemorrhage (ICH) that can occur in utero

Epidemiology

Epidemiology

Epidemiology

1:1,000 live births

General Prevention

General Prevention

General Prevention

In pregnancies known to be at risk of NAIT, maternal treatment with IVIG in the antenatal period can be considered.

Pathophysiology

Pathophysiology

Pathophysiology

Antibody-mediated platelet destruction

Etiology

Etiology

Etiology

Maternal IgG antibodies, directed against paternally inherited platelet-specific antigens in the fetus, cross the placenta, enter the fetal circulation, and attack fetal platelets.

  • HPA-1a (formerly PLA-1) incompatibility is by far the most common cause of NAIT in those of Caucasian ancestry, accounting for ~75% of cases. The disease happens when the mother is HPA-1a negative (HPA 1b/1b) and father is HPA-1a positive (HPA 1a/1a or 1a/1b). If the fetus inherits HPA-1a from father, maternal exposure to HPA-1a–positive fetal platelets during pregnancy causes mother to generate anti–HPA-1a IgG antibodies. Anti–HPA-1a antibodies crosses the placenta and causes platelet destruction.
  • Other common antigens implicated in NAIT include HPA-2, HPA-3, HPA-5, HPA-9, and HPA-15.
  • HPA-4 incompatibility accounts for the majority of cases in Asian populations.
  • At least 23 other low-frequency antigens have been reported in a small fraction of cases.
  • HPA-1a–negative mothers who are HLA-DRB3*0101 positive are far more likely to develop antibodies than those who are DRB3 negative.
  • The role of HLA platelet antigens in NAIT is controversial.

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