P017 The first case of neonatal alloimmune thrombocytopenia due to HLA antibodies in Hong Kong

Abstract

We report the first case of neonatal alloimmune thrombocytopenia (NAIT) secondary to anti-HLA antibody in Hong Kong. The baby girl was born at 39 weeks gestation by spontaneous delivery, with a birth weight at 4.165 kg. She was kept in hospital for investigations of large for gestational age. A full blood count incidentally showed: moderate thrombocytopenia (Platelets, 64 × 10 9 /L), but normal leukocyte count and haemoglobin. No red cell fragments or spherocytes nor platelet clumps were noted. Over the next two days, her platelet count dropped to 8.0 × 10 9 /L on Day 2, but there were no major bleeding. Her and her mother’s blood groups were both B + and direct antiglobulin test was negative. Antibody screen was negative on the maternal serum. Her mother did not have thrombocytopenia. In view of her marked thrombocytopenia, she was transfused one unit of random donor group B + platelet concentrate and IVIG 4.2 g, and the platelet count rose to 98 × 10 9 /L on Day 3. The mother had no history of blood transfusion. No anti-HPA antibodies were detected by antigen-captured ELISA. Maternal serum was crossmatch incompatible with father’s platelets by PIFT. Luminex SAB test demonstrated broad spectrum anti-HLA IgG antibodies with 2,000–5,000 MFI against several HLA-A, -B antigens in the maternal serum, and NAIT caused by HLA antibodies was suspected. Anti-A203 and anti-B55 IgG antibodies were found against the paternal inherited HLA antigens. These specific antibodies with 1,500–2,000 MFI were also detected in her pre-treatment serum. Although the initial platelet response was satisfactory, the platelet count gradually dropped again from 82 × 10 9 /L on Day 4 to 49 × 10 9 /L on Day 7. She was then given further IVIG 4.2 g with the platelet count rose to 79 × 10 9 /L on Day 8. The platelet count then stabilized up to Day 10. Although the mother was a primipara, anti-HLA antibodies could still occur since even non-transfused men may have ‘naturally occurring’ anti-HLA antibodies. Based on the anti-HLA antibodies in the maternal serum, the mother’s and baby’s HLA typing results and the PIFT results, we believe that there is evidence this is a rare and unique case of NAIT secondary to anti-HLA antibodies.