title: HPA-1a antibody potency and bioactivity do not predict severity of fetomaternal alloimmune thrombocytopenia.
abstract: BACKGROUND
  The antenatal management of fetomaternal alloimmune thrombocytopenia (FMAIT) due to HPA-1a antibodies remains controversial, and a test identifying pregnancies that do not require therapy would be of clinical value.
  
  
  METHODS
  The statistical correlation was analyzed between clinical outcome and 1) anti-HPA-1a potency in maternal serum samples determined by a monoclonal antibody immobilization of platelet (PLT) antigen assay with an international anti-HPA-1a potency standard and 2) anti-HPA-1a biological activity measured by a monocyte chemiluminescence (CL) assay.
  
  
  RESULTS
  A total of 133 pregnancies with FMAIT due to anti-HPA-1a were analyzed. In 97 newly diagnosed cases, there was no difference in antibody potency or CL signal between cases with intracranial hemorrhage (ICH; n = 15), those with no ICH but a PLT count of less than 20 x 10(9) per L (n = 52), and those with a PLT count of at least 20 x 10(9) per L (n = 30). In 22 previously known pregnancies, the positive predictive value of maternal anti-HPA-1a of greater than 30 IU per mL for a PLT count of less than 20 x 10(9) per L was 90 percent, but the negative predictive value was only 66 percent. Antibody potency tended to stay stable throughout pregnancy (n = 16) and from one pregnancy to the next (n = 16).
  
  
  CONCLUSIONS
  Neither severe thrombocytopenia nor ICH in HPA-1a-alloimmunized pregnancies can be predicted with sufficient sensitivity and specificity for clinical application from maternal anti-HPA-1a potency or bioactivity.
authors.affiliation: National Blood Service, Department of Haematology, University of Cambridge, Cambridge, UK. cedric.ghevaert@nbs.nhs.uk
authors.forename: Cedric
authors.initials: C
authors.lastname: Ghevaert
authors.forename: Kate
authors.initials: K
authors.lastname: Campbell
authors.forename: Prachi
authors.initials: P
authors.lastname: Stafford
authors.forename: Paul
authors.initials: P
authors.lastname: Metcalfe
authors.forename: Angela
authors.initials: A
authors.lastname: Casbard
authors.forename: Graham A
authors.initials: GA
authors.lastname: Smith
authors.forename: Dave
authors.initials: D
authors.lastname: Allen
authors.forename: Edmund
authors.initials: E
authors.lastname: Ranasinghe
authors.forename: Lorna M
authors.initials: LM
authors.lastname: Williamson
authors.forename: Willem H
authors.initials: WH
authors.lastname: Ouwehand
mesh_terms: D000328:Adult; D016824:Antigens, Human Platelet / Q000276:immunology*; D005260:Female; D005331:Fetomaternal Transfusion / Q000150:complications*; D006801:Humans; D039661:Integrin beta3; D020300:Intracranial Hemorrhages / Q000175:diagnosis; D007518:Isoantibodies / Q000097:blood*; D010976:Platelet Count; D011237:Predictive Value of Tests; D011247:Pregnancy; D011256:Pregnancy Outcome; D011296:Prenatal Diagnosis; D012720:Severity of Illness Index; D013921:Thrombocytopenia / Q000175:diagnosis* / Q000276:immunology
chemical_list: D016824:Antigens, Human Platelet; C061248:ITGB3 protein, human; D039661:Integrin beta3; D007518:Isoantibodies