Management of severe alloimmune thrombocytopenia in the newborn
- Division of Transfusion Medicine, University of Cambridge and National Blood Service, Cambridge CB2 2PT, UK
- Dr Ouwehand
Petechiae or echymoses and severe thrombocytopenia (< 20 × 109 platelets/litre) is a worrying and serious condition in newborn infants. Rapid correction of the platelet count is essential to prevent cerebral bleeding and associated life long disability, and this should be combined with laboratory investigations to confirm the clinical diagnosis. Prospective studies have revealed that the most likely cause of severe thrombocytopenia in a term and otherwise healthy neonate is immune mediated destruction of fetal/neonatal platelets by maternal alloantibodies.1 2Antibodies can be formed against human platelet alloantigens (HPAs)3 4 present on fetal but not maternal platelets (table 1). Leakage of fetal platelets and possibly other HPA alloantigen expressing fetal cells5 into the maternal circulation during pregnancy can stimulate the mother's immune system to produce IgG alloantibodies against “non-self” HPAs inherited from the father. Maternal HPA alloantibodies of the IgG class cross the placenta and bind to fetal platelets, shortening their survival.
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Clinically most relevant human platelet alloantigen (HPA) systems associated with neonatal alloimmune thrombocytopenia
Is neonatal alloimmune thrombocytopenia a rare disease?
Neonatal alloimmune thrombocytopenia is the platelet homologue of haemolytic disease of the newborn and was initially thought to be a rare disease. However, a recent prospective screening study in 25 000 non-selected pregnant women showed an incidence of severe thrombocytopenia (< 50 × 109 platelets/litre) caused by anti-HPA-1a antibodies (see below) of one in 1100 (95% confidence interval, 684 to 2910).6 No antenatal screening procedure is in place to identify women at risk of HPA alloimmunisation because it has not been proved that this would significantly reduce morbidity and mortality.6 Thus, neonatal alloimmune thrombocytopenia is diagnosed in utero if a pregnancy is complicated (for example, cerebral bleeds, hydrocephalus,7 8 or hydrops fetalis) or in the newborn by obvious signs of bleeding or abnormal neurological features pointing towards a possible cerebral bleed.3 4Infrequently, …
