September 2020 — Transfusion Medicine

A 49-year-old female with FLT3+ AML became refractory to platelet transfusions 2 weeks after initiating chemotherapy with venetoclax, midostaurin, and corticosteroids. A solid phase single antigen bead (SAB) assay demonstrated the patient had an antibody to all HLA-B antigens sharing the Bw6 epitope. Subsequently, she was given IVIG to help bolster her platelet counts. A solid phase red blood cell adherence platelet crossmatch was performed and a unit homozygous for Bw4 class antigens was unexpectedly incompatible (image; right columns of wells). Repeat testing performed on a prior sample showed the unit was compatible (image; left columns of wells).

Which of the following agents/drugs could lead to a false positive crossmatch?

  • Assay interference by IVIG
  • Assay interference by venetoclax
  • Assay interference by midostaurin
  • Assay interference by corticosteroids

The correct answer is...

The correct answer is Assay interference by IVIG.

IVIG is manufactured by pooling plasma from a large number of donors, some of which can have HLA antibodies. The IVIG present in a patient’s sample can bind to the HLA antigens on the platelets utilized in a platelet crossmatch creating a positive (incompatible) result. Thus, the binding of HLA antibodies contained within the IVIG can cause an erroneously false positive crossmatch result. The other agents/drugs do not cause interference with the platelet crossmatch assay.

1. Immucor Capture-P® Solid Phase System for the Detection of IgG Antibodies to Platelets package insert; version 340-14.

Photo of Holly Berg, D.O. Holly Berg, D.O.
Resident, Anatomic and Clinical Pathology
Mayo Clinic
Photo of Linda Justin Juskewitch, M.D., Ph.D. Justin Juskewitch, M.D., Ph.D.
Senior Associate Consultant, Transfusion Medicine
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

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