Laboratory testing for platelet antibodies

Abstract

Laboratory testing for immune-mediated thrombocytopenias involves identification and classification of antibodies present in patient sera or attached to patient platelets. This article summarizes the available types of platelet antibody testing and applications in disorders such as neonatal alloimmune thrombocytopenia, post-transfusion purpura, multiple platelet transfusion refractoriness, immune thrombocytopenia, and drug-induced thrombocytopenia. Am. J.

Phase 2 study of efgartigimod, a novel FcRn antagonist, in adult patients with primary immune thrombocytopenia

“…However, no apparent correlation with the extent of the clinical effect could be observed, which could possibly be due to the small sample size and the inherent autoantibody assay limitations in ITP. 42 Efgartigimod-treated groups achieved a higher maximum mean platelet count change from baseline compared to the placebo group.…”

“…Targeting FcRn with efgartigimod resulted in rapid and selective IgG reduction, and a greater numerical reduction was observed in the efgartigimod 10 mg/kg group, without impacting the levels of other immunoglobulin isotypes. 42 Efgartigimod-treated groups achieved a higher maximum mean platelet count change from baseline compared to the placebo group. 39 Notably, efgartigimod administration did not result in a reduction of albumin levels, which has been observed with some anti-FcRn monoclonal antibodies, 40,41 suggesting that the Fc fragment efgartigimod is not interfering with albumin binding or influencing the fate of FcRn.…”

Severe thrombocytopenia in a patient following liver transplantation caused by HPA‐1a antibodies produced by the liver donor

“…The patient was exposed to multiple blood products and investigation for post‐transfusion purpura (PTP) and alloimmune thrombocytopenia were performed. In PTP, increased platelet clearance and thrombocytopenia occur when a HPA‐1a negative recipient develops anti‐HPA‐1a alloantibodies 7–10 days after receiving a blood product containing platelets or platelet membranes from a HPA‐1a positive donor . It is interesting that platelet clearance in PTP involves autologous as well as transfused platelets and is caused by autoantibodies that form concomitantly with the potent HPA‐1a alloantibodies …”

Intravenous immunoglobulin–induced acute thrombocytopenia

“…PIFT was used to screen for PLT-associated antibodies (direct PIFT) and anti-PLT antibodies in patient's plasma and/or IVIG (indirect PIFT), as previously described. 13,14 Patient's PLTs were prepared from PLT-rich plasma (PRP) by centrifugation of 6 mL of patient's anticoagulated whole blood (in EDTA) at 800 3 g for 20 minutes, washed twice with normal saline at 13,000 3 g for 5 minutes, and resuspended in saline to a final concentration of 100 3 10 6 cells/mL. Control PLTs were obtained from a pool of 1.2 mL of PRP from three group O random PLT units (200 mL/unit).…”