Hemoglobin S target of <50% as compared to 30% in chronic red cell exchange for secondary stroke prevention in sickle cell disease

Background: Sickle cell disease (SCD) patients with a history of stroke are encouraged to receive chronic red blood cell exchange (RBCx) for stroke prevention. The American Society of Hematology guideline published in 2020 recommends an HbS target of <30%. However, this approach necessitates more frequent RBCx and more RBC units. UT Southwestern has devised a chronic exchange protocol that elevates the HbS target to <50% in patients with a low risk of stroke. Study Design: This retrospective chart review study reviewed the medical records of patients receiving chronic RBCx with a target of HbS <50% over the past 10-year period to assess the safety of maintaining higher HbS targets in SCD patients with a low risk of cerebrovascular accidents (CVA). Results: Among 49 SCD patients in the chronic RBCx program for secondary stroke prevention, 33 patients were maintained on an HbS target of <50% (average measured: 35.4%) for the duration of RBCx program enrollment (median 93.0 months, 95% CI, 83-99). Stroke or transient ischemic attack (TIA) clearly attributable to changing target HbS had not been identified among the 33 study subjects. Seven patients experienced conversion between the HbS targets of <50% and <30% HbS target. Significant reductions were observed in the frequency of RBCx and usage of blood volume in four of them. Conclusion: The findings suggest that liberalizing the HbS target could confer clinical flexibility without increasing the risk of CVA in a selective population. Further studies to fully evaluate the potential benefits of this approach are indicated.