HPA-1a antibody potency and bioactivity do not predict severity of fetomaternal alloimmune thrombocytopenia.
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.
Ghevaert
Cedric
C
National Blood Service, Department of Haematology, University of Cambridge, Cambridge, UK. cedric.ghevaert@nbs.nhs.uk
Campbell
Kate
K
Stafford
Prachi
P
Metcalfe
Paul
P
Casbard
Angela
A
Smith
Graham A
GA
Allen
Dave
D
Ranasinghe
Edmund
E
Williamson
Lorna M
LM
Ouwehand
Willem H
WH
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
D016824:Antigens, Human Platelet; C061248:ITGB3 protein, human; D039661:Integrin beta3; D007518:Isoantibodies