A WHOLE-BLOOD ASSAY FOR PLATELET HPA1 (PLA1) PHENOTYPING APPLICABLE TO LARGE-SCALE SCREENING

Any future programme of antenatal screening of pregnancies for risk of neonatal alloimmune thrombocytopenia will have as a major requirement the availability of cost-effective assays which can be applied to lar ge numbers of samples. To address this, we developed a competitive ELI SA to type whole blood samples for the platelet alloantigen HPA1a, bas ed on the use of purified glycoprotein (GP) IIb/IIIa from donors of kn own HPA1 genotype along with well characterized anti-HPA1a antiserum, Microtitre plates were coated with purified GPIIb/IIIa from donors of genotype HPA1a1a/3a3a. Anticoagulated whole blood of unknown HPA1 type was added to each well followed by anti-HPA1a. Residual antiHPA1a ant ibody not bound to the platelets in the test blood sample, bound to th e immobilized HPA1a on the plate and was quantitated by standard ELISA . 475 blood donors were typed by the assay and the results compared in a blinded comparison with typing in the Capture-P-tm assay. Concordan ce was 100% (468 HPA1a positive and seven HPA1a negative). The HPA1 ty pe of control samples stored as whole blood could be discriminated by this assay for up to 23 d of storage at 4 degrees C. This assay should be suitable for use in large-scale population screening programmes.