Neonatal alloimmune thrombocytopenia involving HPA-5b (Br(a)): a rare Japanese case

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.

Anti-HPA-5b-induced neonatal alloimmune thrombocytopenia: antibody titre as a predictor. Collaborative Study Group

Anti-HPA-5b is the most commonly found platelet-specific antibody among pregnant women, but it does not cause severe fetal-neonatal alloimmune thrombocytopenia in the majority of affected infants. However, as the sequelae of the affected children may become severe, it is necessary to identify the risk factors for neonatal alloimmune thrombocytopenia. Of 21 354 consecutive pregnant women, 138 [0.65%; 95% confidence interval (CI) 0.54-0.75%], corresponding to 13.2% of the 1049 HPA-5b- women calculated by the gene frequency, were positive for anti-HPA-5b at the first trimester. Anti-HPA-5b was titrated in specimens obtained at the third trimester and antibody-positive women and their neonates were HPA-5 genotyped. Platelet counts in cord blood and 3 d after birth were assessed in the infants born to these mothers. Chi-square analysis showed no significant relationship between the titres of maternal antibody to HPA-5b and the number of pregnancies. There was a significant difference in platelet counts at d 3 between neonates who were compatible (267 x 109/l) or incompatible (220 x 109/l, P < 0.05) with maternal anti-HPA-5b. HPA-5b antibody titres >/= 64 were related to the development of thrombocytopenia (< 150 x 109/l) in neonates 1 d and 3 d after birth. A high titre (>/= 64) had a positive predictive value of 50% for thrombocytopenia 3 d after birth when the infant was HPA-5b+ and a negative predictive value of 100%. These results indicate that a high titre (>/= 64) of anti-HPA-5b is associated with a higher risk of neonatal thrombocytopenia, even if anti-HPA-5b-induced severe thrombocytopenia rarely develops.