(P-TS-48) Evaluating Platelet Refractoriness in Pediatric Patients: A Single Site Retrospective Experience

Background/Case Studies: Platelet transfusion refractoriness (PTR) occurs in 60% of adult patients undergoing hematopoietic stem cell transplantation (HSCT). However, there is limited data on PTR incidence, investigation or approach to management in pediatric patients.

Study

Design/Methods: An IRB approved retrospective chart review was performed on all patients consulted for PTR evaluations from January 1, 2021- December 31, 2024.

Results/Findings: Forty-three patients were identified. There was a slight predominance of myeloid malignancy. Sixteen patients (37.2%) received prior HSCT and/or CAR-T. Of the HSCT recipients, 1 received >1 transplant (7.7%) with the majority receiving matched unrelated donor grafts (Table 1).



HLA antibody screening was performed on all patients. Nineteen of 43 (44.2%) were positive. The HLA antibody identification assay did not correlate with the HLA antibody screen. Of the 5 patients with cPRA% for HLA antibodies < 20%, 1 (20%) had a negative HLA screen. Fourteen (73.7%) patients with positive HLA antibody screen had specific antibody(ies) identified. Five patients with positive HLA antibody screens were reported negative by a single antigen bead assay for antibody identification. These discrepancies were likely due to low levels of reactivity present below the MFI threshold for clinical significance or reactivity outside of the capacity for this test to detect, such as autoantibodies or rare alloantibodies.



HPA antibody screening was performed on 28 patients (65.1%), 5 (17.8%) of which were positive. Antibodies identified were to GPIIb-IIIa (2 patients) and GPIIIb-IIIa (1 patient). Platelet crossmatch demonstrated 100% incompatibility for both patients with anti-GPIIb-IIIa. Two patients with positive screen had no platelet antibody(ies) identified but had 9 and 10 out of 14 platelets incompatible with donor platelets.



Platelet crossmatch was performed in 24 (55.8%) patients. The majority of those patients (79.2%) were compatible with < 50% of random donor platelets tested. A subgroup of 7 patients (29.2%) demonstrated incompatibility (mean 9.9 units, median 12 units/14 units tested), negative HLA/HPA antibody screen, and negative HLA single antigen bead testing. Only 1 patient in this subgroup had 0% incompatibility. One patient with negative HLA/HPA antibody screen and 100% crossmatch incompatibility had drug dependent platelet antibody testing, which was negative.

Conclusions: One third of the patients that received platelet crossmatch had significant incompatibility in vitro, with a negative HLA/HPA antibody screen, and negative HLA single antigen bead screening, with no identifiable immunology or disease associated cause. Comprehensive testing for PTR should include crossmatch in addition to antibody screening, particularly in patients with incongruent testing and in vivo platelet performance.