Impact of Voxelotor on Red Blood Cell Exchange Therapeutic Procedures: Evaluation of Multi-Institutional Procedure Data

Hemoglobin S (HbS) polymerization inhibitor drugs such as voxelotor can result in a split peak in HbS as well as additional peaks with hemoglobin A in quantitative methods of HbS measurement. It is unclear how these results should be used to make transfusion decisions. The goal of this study is to compare RBC exchange (RBCX) replacement volumes calculated with HbS-Vox + HbS versus HbS alone. Patients aged 15–58 years who had variant hemoglobin quantitation performed for clinical care purposes with evidence of voxelotor treatment (split peak in HbS and/or additional peaks with hemoglobin A) were identified by investigator review of variant hemoglobin quantitation test results from the clinical laboratory. The RBCX replacement volume calculated with HbS% total (RBCX volume HbS% total) was compared to the RBCX replacement volume calculated with HbS unmod% (RBCX volume HbS unmod%) in each case. The mean difference between RBCX volume total HbS% and RBCX volume HbS% unmod is 398 mL with 95% CI (198, 598) and RBCX volume total HbS is significantly different from RBCX volume HbS unmod (p value = 0.0006). If the HbS total is not used to calculate RBCX replacement volumes in patients taking voxelotor, there is a significantly lower amount of RBC that would be ordered, which would lead to higher HbS after RBCX. Additional studies regarding the role of transfusion in such patients are necessary.