Edinburgh Napier University

  Background: The great majority of severe NAIT is due to HPA-1a antibodies (ab). However, due to uncertainties in clinical management and health economics, HPA-1 phenotyping of pregnant women is not currently undertaken.
Aims of Study: The aims of this national study in Scotland were to determine (1) the frequency of HPA-1b and anti-HPA-1a; (2) the incidence of NAIT and the extent to which it is under-diagnosed; and (3) to carry out a health economic evaluation. Methods: 26,506 pregnant women were screened for their HPA-1 type using a whole blood ELISA. Those found to be HPA-1b were typed again by ELISA and PCR and, once confirmed as HPA-1b, their HLA DRB3*01 type and anti-HPA-1a status during pregnancy were determined using PCR and a direct ab ELISA respectively. Based on the current cost of no screening, the costs of two options were evaluated:
The screening of all previously unaffected women and genotyping the partners of all HPA-1b women (option 1), or the partners of only HPA-1b women who develop abs (option 2). Results: Excluding initial mistypes, 453 women
(1.7%) were HPA-1b, of whom 327 (72%) consented to follow up. Twentyeight women (8.8%) were found to be positive for anti-HPA-1a and of these 8 (32%) gave birth to babies with NAIT, 5 of whom were severe. Four of these babies required one or two prompt HPA-1b platelet transfusions. Intracranial haemorrhage was not reported. There was a significant correlation between DRB3*01 type and ab production (P < 0.01). The calculated annual incidence of mild and severe NAIT in our study was 4.1 and 2.6 per 10,000 pregnant women respectively, compared to 1/10,000 detected (presumably severe) in routine clinical care. Finally, option 2 was found to be
more cost-effective, with an incremental cost per NAIT case detected of £22,936 and per severe NAIT case detected of £57,340. Conclusions: The frequnecies of HPA-1b and anti-HPA-1a in Scotland are at the lower end of
the spectrum. Our study indicates that 75% and 60% more cases of NAIT and severe NAIT respectively may be diagnosed by routine antenatal screeening, and that option 2 would be a more cost-effective approach for screening.