Delayed detectability of anti-HPA-3a by the MAIPA assay in a severe neonatal alloimmune thrombocytopenia, but successful transfusion of incompatible donor platelets: a case report.

Fetal/neonatal alloimmune thrombocytopenia (F/NAIT) is the most frequent cause of haemorrhagic morbidity and mortality in otherwise healthy term infants and occurs in 1 in 1000 to 1 in 2000 pregnancies [1]. Maternal HPA-1a alloimmunization is responsible for the majority of NAIT [1], and only a few cases of NAIT caused by anti-HPA-3a have been published [2–4]. However, based on gene frequencies of HPA-3 in Caucasoids [5], HPA-3 alloimmunization is potentially the most frequent cause of NAIT. Thus, this antigen system may be of minor antigeneicity. Alternatively, the frequency of HPA-3 antibodies may be underestimated as a result of difficulties in their detection [2,3]. We describe a term newborn with NAIT caused by antiHPA-3a; however, serological proof from the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay was delayed for 6 months. Although compatible donor platelets are recommended for NAIT, unmatched platelets were transfused without adverse effects and this led to a transient increase of platelet counts. A second transfusion of a platelet concentrate, matched for the maternal HPA-3 allotype, led to a persistent platelet increment above 50 000/ μ l. Thus, in suspected NAIT, platelet transfusions may not need to be delayed until serological results are available.