Estimation of post-transfusion HbA level is relevant after RBC exchange in sickle cell adult patients

Abstract Background Transfusion (TF), or exchange transfusion (ExTF), is a major therapy for sickle cell disease (SCD) patients. However, these transfusions can lead to complications, including Delayed Hemolytic Transfusion Reaction (DHTR), which occurs in 4–11% of cases and leads to the hemolysis and rapid disappearance of transfused red blood cells. Since SCD patients are unable to produce HbA, post-transfusion HbA levels can be used to assess the efficacy of TF. Monitoring the disappearance of HbA mass after RBCs transfusion by means of the “DHTR nomogram” is currently used for the diagnosis of DHTR in our reference center. However, this method is not widely used due to a lack of post-transfusion biological tests, particularly for HbA. Clinicians usually check routinely post-transfusion Hemoglobin (Hb), but not the % of HbA . The aim of this study was to better determine the immediate post TF percentage of HbA per unit of transfused Red Blood Cells(RBCs) in SCD adult patients. Methods In this single center retrospective study, biological data from SCD adult patients who had undergone ExTF or TF, either at the initiation of their TF program or during an acute complication were collected. Eligible patients were adults SCD patient with no recent (<3 month) TF confirmed by the French blood bank center with available Hb electrophoresis. According to French SCD guidelines, all patients received two units of RBCs, with or without prior phlebotomy. HbA levels (as measured by high-performance liquid chromatography with cation exchange) were measured within 48 hours of the procedure. All participants provided informed consent to participate in the study. Results We retrospectively collected data from 84 cases of ExTF or TF performed in our hospital. Among these, 81 patients had homozygous sickle cell disease (SS) and 3 had Sβ⁰-thalassemia. The cohort included 47 men and 37 women, with a median age of 37 years [IQR: 27–41] and a median weight of 68 kg [IQR: 60–78] at time of ExTF or TF. ExTF or TF was performed during acute complication in 36 patients and at the initiation of a TF program in 48 patients. The median pre-transfusion Hb level was 7.9 g/dL [IQR: 6.8–9.1], increasing to 9.4 g/dL [IQR: 8.4–10.3] after the TF / ExTF . The level of HbA rose from 0% (pre TF/ETF) to 22.7% [IQR: 20.0–24.8] after two RBC units. To evaluate the impact of pre-transfusion hemoglobin levels on TF efficiency, patients were stratified into four groups: Hb < 7 g/dL, 7–8.4 g/dL, 8.5–9.5 g/dL, and > 9.6 g/dL. Following the recommended bleeding volumes provided by our center. The HbA gain per RBC unit was as follows: • 12.3% [IQR: 11.2–13.8] for the group with Hb < 7 g/dl, and a post TF at 8,1[7,7-8,4]g/dl • 11.2% [IQR: 10.1–12.3] for the group with Hb 7–8.4 g/dl and a post TF at 9,2[8,7-9,8]g/dl • 11.3% [IQR: 10.2–11.9] for the group with Hb 8.5–9.5 g/dl and a post TF at 10,3[9,6-10,5]g/dl • 10.3% [IQR: 9.4–12.3] for the group with Hb > 9.6 g/dl and a post TF at 10,7[10,4-11,2]g/dl These results show that the HbA level remains relatively stable across different pre-TF Hb levels. And Post TF HB levels are optimized. Conclusion This provides some new evidence showing that estimating the percentage of HbA after TF or ExTF is a reliable and stable marker in SCD adult patients. Based on these results, HbA level after two RBC units ranges from 22% to 24%, suggesting that each unit contributes approximately for 10- 12%. The lower the pre-transfusion Hb level, the higher the resulting HbA percentage. The homogeneity of the results must encourage clinicians to use this parameter and the DHTR nomogram that was previously published (American Journal of Hematology, Vol. 00, No. 00, Month 2016) in order to detect as soon as possible the onset of DHTR. Furthermore, the combination of phlebotomy and the transfusion of two RBC units, as recommended in the French guidelines, appears to optimize Hb level. This strategy helps avoid increasing Hb in patients with higher Hb level and the risk of hyperviscosity , as well as significant Hb rises in patients with lower pretransfusion Hb levels. .