Rationale: Neonatal alloimmune thrombocytopenia (NAIT) caused by anti HPA-3a antibody is rare, and the clinical features of the syndrome are not specific.
Patient concerns: A male infant was noted to be irritable and physical examination revealed the presence of petechiae and bruising on the right arm and thigh after born.
Diagnoses: Platelet antibodies were investigated using the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay, platelet genotyping (HPA 1-17) was performed by polymerase chain reaction technique with sequence-specific primers (PCR-SSP). The HPA genotype of the newborn was HPA-3a/b, while that of his mother and his father were HPA-3b/b and HPA-3a/a, respectively. The sera of newborn contained antibody against the platelet of newborn's father. The HPA antibody of the newborn was identified as anti HPA-3a. The newborn was confirmed as a patient of NAIT caused by anti HPA-3a antibody.
Interventions: A single dose of intravenous immunoglobulin (IVIG) 1 g/kg was administered from day 3 to day 7.
Outcomes: At follow-up 3 months after discharge from the hospital, the baby was developing normally and had a normal platelet count (361 × 109/L).
Lessons: NAIT caused by anti HPA-3a antibody is rare, and we believe this study can provide insights for diagnosing prospective cases. Prognosis of NAIT caused by HPA3a seems to be favorable if diagnosed and treated in a timely manner.