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