Neonatal alloimmune thrombocytopenia associated with anti-human platelet antigen-3a antibody

Timely diagnosis and treatment of neonatal alloimmune thrombocytopenia caused by anti HPA-3a antibody: A case report

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.

Anti-HPA-3A induces severe neonatal alloimmune thrombocytopenia

OBJECTIVE

Fetal and neonatal alloimmune thrombocytopenia (AIT) caused by feto-maternal incompatibility at the HPA-1a (PLA-1) locus is well characterized. Alloimmunization and disease caused by HPA-3a is rare.

STUDY DESIGN

We conducted a retrospective analysis of all known cases of AIT caused by HPA-3a incompatibility identified at 3 major reference laboratories from 1986 to 1996. Platelet antigen typing and antibody specificity were determined by serologic evaluation. In some cases confirmatory genotyping was performed.

RESULTS

Fourteen cases of anti-HPA-3a-induced AIT in 11 families were identified. Five patients had a previous affected sibling, and 2 cases were firstborn children. All patients had severe thrombocytopenia at birth (platelet count <20 x 10(9)/L). Regardless of therapy, the median time to platelet recovery was 6 days (range, 3 to 23 days). Two (15%) patients had documented intracranial hemorrhage, 1 with severe sequelae including apnea and convulsions. A literature review describing 16 additional patients corroborates the finding of severe thrombocytopenia and a significant incidence of intracranial hemorrhage caused by HPA-3a incompatibility.

CONCLUSION

AIT caused by incompatibility of HPA-3a is similar in severity to disease caused by incompatibility of HPA-1a. Affected families should be appropriately counseled and considered for antenatal therapy.

Feto-maternal alloimmune thrombocytopenia: a literature review and statistical analysis

Exploring prognostic factors that determine outcomes in fetomaternal alloimmune thrombocytopenia (FMAIT), a search of Medline was performed covering the years 1966 to April 1998. 376 articles were collected and reviewed; 140 articles contained the case histories of 297 mothers and 433 pregnancies that fulfilled entry criteria. More than 30 data variables were sought from these cases. The data were analysed using SPSS and Arcus Quickstat Biomedical. Nineteen different antigen incompatibilities were documented, the majority being human platelet antigen (HPA)-1a (77.3%), HPA-3a (3.5%) and HPA-5b (3.5%). The relative risk reduction (RRR) in mortality with any intervention was 57% (0.19-0.77) p = 0.009. Treatment of HPA-1a (PlA1) pregnancies with intravenous immunoglobulin (IVIG) increased the likelihood of a neurologically normal outcome, relative risk (RR) 1.68, confidence interval (1.3-2.2) p = 0.0003. Treatment of HPA-1a (PlA1) pregnancies with only antenatal complementary platelet transfusions increased the likelihood of a neurologically normal outcome, RR 1.63 (1.1-2.1) p = 0.01. Despite reviews of more than 400 cases of FMAIT, few prognostic variables are identifiable. Although IVIG appears to reduce the risk of intracranial haemorrhage (ICH), the dosage and timing of IVIG treatment was varied. This study highlights the need for standardised and directed research.

The management of alloimmune neonatal thrombocytopenia

Neonatal alloimmune thrombocytopenia (NAITP), defined as thrombocytopenia (platelet count < 150 x 10(9)/l) due to transplacentally acquired maternal platelet alloantibodies, occurs in approximately 1 per 1200 live births in a Caucasian population. In such a population, the majority (> 75 percent) of cases are due to fetomaternal incompatibility for the platelet specific alloantigen, HPA-1a (P1A1, Zwa). Incompatibility for the HPA-5b (Bra) alloantigen is the next most frequent cause of NAITP in Caucasians; much less common is NAITP due to incompatibility for HLA, blood group ABO or other platelet-specific antigens. In non-Caucasian populations (e.g. Orientals) HPA-1a incompatibility is a rare cause of NAITP and other alloantigens e.g. HPA-4b (Penb, Yuka) are implicated. The greatest clinical challenge relates to the antenatal management of pregnant women alloimmunized to the HPA-1a (P1A1, Zwa) antigen, and particularly the subset of such women who have a history of a previously affected infant with severe thrombocytopenia and/or intracranial hemorrhage (ICH). The risk of antenatal ICH in the fetus of such women is high enough to merit intervention, either weekly infusion of high-dose intravenous immunoglobulin G (IVIG) with or without corticosteroids given to the mother (the preferred approach in North American centres), or repeated in-utero fetal platelet transfusions (the preferred treatment approach in some European centres). Post-natal management of severely affected infants centres on the rapid provision of compatible antigen-negative platelets harvested from the mother or a phenotyped donor. The value of antenatal screening programs to detect 'at risk' alloimmunized women during pregnancy continues to be debated.