Investigating human platelet antigens and antibodies in pregnancy: An 11‐year experience from a Canadian reference laboratory

BACKGROUND AND OBJECTIVES: Foetal and neonatal alloimmune thrombocytopaenia (FNAIT) is a potentially severe immune-mediated condition that is believed to be under-identified in the Canadian population. The Canadian Blood Services National Platelet Immunology Reference Laboratory (NPIRL) serves as a centralized referral laboratory for FNAIT investigations across Canada. Diagnostic evaluation includes human platelet antigen (HPA) genotyping and maternal anti-HPA antibody testing. This study is a review of all FNAIT investigations referred to NPIRL to assess testing patterns, antibody detection rates and evidence of under identification at a national level. MATERIALS AND METHODS: All maternal, paternal and neonatal samples related to FNAIT investigations between 20 January 2014 and 31 December 2024 were extracted from the NPIRL database. The geographic origin of samples, HPA genotyping and antibody specificity, if present, were documented. RESULTS: A total of 1986 samples (1076 maternal, 620 paternal and 290 neonatal) were received for FNAIT investigation over the 11-year study period. One-hundred and thirty-five HPA antibodies were identified in 130 of the maternal samples tested, with anti-HPA-1a and HPA-5b being the most frequently detected specificities. Despite a modest increase in annual referrals, the total number of investigations and antibody-positive cases was substantially lower than expected based on Canadian birth rates and published FNAIT incidence estimates. CONCLUSION: Referral patterns and laboratory findings from NPIRL demonstrate a marked discrepancy between expected FNAIT incidence and observed diagnostic activity in Canada, indicating that FNAIT is substantially under-identified. These findings highlight the need for improved recognition, standardized investigation pathways and enhanced diagnostic strategies to reduce missed cases and improve neonatal outcomes.