Post-Exchange Transfusion Hematocrit in Sickle Cell Disease and Vaso-occlusive Complications
Authors: Rizvi Insia , Gordeuk Victor R , Molokie Robert , Zhang Xu , Allison David , Saraf Santosh L , Farooqui Marwah , Njoku Franklin 
Published: June 2024

Abstract

Presentation Date: 6/9/2024
Presentation Start Time: 2:27:00 PM

Background
Sickle cell disease (SCD) is associated with a decrease in the quality of life and its expectancy. Automated red cell exchange (RCE) plays a key role in the management of SCD, with the goals of ameliorating and preventing vaso-occlusion while preserving organ function. RCE is used for primary and secondary prevention of stroke and acute chest syndrome. RBC units have additive solution with a hematocrit of about 60% but can vary between each unit. The impact of fluid compartment equilibration due to this additive solution may lead to lower hematocrit immediately post-exchange. Hence, this lower immediate post exchange hematocrit should be compared with hematocrit measurements after fluid compartment equilibration in ensuing hours to days. The intended benefits of exchange transfusion may be offset by an increased hematocrit leading to increased viscosity and an associated increased risk of vaso-occlusive complications. Our aim is to review pre and post RCE hematocrits and their relationship to vaso-occlusive complications within 30 days of exchange. An increase in hematocrit in the days after RCE would suggest that there is hemodilution during the exchange.

Methods
This is a single institution retrospective cohort study of SCD patients who had RCE transfusions from June 1, 2015 until March 31, 2023. Inclusion criteria included &gt;18 years with genotypes HbSS/HbSβ○/HbSβ+/HbSC. Data collected included: indication for RCE, age, sex, weight, height, medical history, sickle genotype, SCD complications, disease modifying therapy, date of service, pre and post exchange hemoglobin electrophoresis, platelets, hemoglobin, hematocrit (pre-exchange, immediate post-exchange, and measurements up to 30 days post-exchange) and SCD-related complications up to 30 days post-RCE, including vaso-occlusive episode (VOE), acute chest syndrome (ACS), venous thromboembolism (VTE), and priapism who had hospitalization, emergency or acute care visits. Statistical methods used to analyze the data are indicated in legends of the figure.

Results
A single RCE was reviewed for 133 patients. 133 pre-RCE hematocrits and 551 hematocrits immediately post-RCE and up to 7 days post-RCE were analyzed and SCD-related complications within 30 days were recorded. 49 patients (37%) experienced complications within 30 days of RCE. Median age was 34 years (interquartile range 28 46), 76 (57%) were females, 110 (84%) with HbSS/HbSβ0 genotypes, and 52 (40%) were on hydroxyurea. There was an increased risk of SCD-related complications within 30 days of transfusion for pre-RCE hematocrit &gt;29% (p = 0.048), immediate post-RCE hematocrit &gt;31% (p = 0.034), and if increment from pre-RCE hematocrit to maximum post-RCE hematocrit was &gt;5% (p = 0.069) (Table 1). Also, a greater slope of post-RCE hematocrits (change of hematocrit over time), suggesting more RCE hemodilution, was associated with an elevated risk for complications within 30 days of transfusion (P = 0.015) (Figure 1).

Conclusions
Our findings suggest that there is an increased risk of SCD-related complications within 30 days of RCE transfusion if the baseline pre-RCE hematocrit is &gt; 29%, if the immediate post-RBC exchange hematocrit is &gt; 31%, if the increment in hematocrit during RCE is &gt; 5% within 7 days, or if there is a greater degree of iatrogenic hemodilution during the RCE process. Thus, the intended benefits of RCE transfusion may be offset by the adverse effects of an increased hematocrit immediately post-RCE or that develops in the days post-RCE. Our study has a large sample size but is limited by being retrospective in nature. Our work is also limited by the inability to control for the multitude of factors that influence VOE risk such as other disease modifying therapies, VOE triggers and the disease itself. These findings suggest it may be important to limit the targeted hematocrit post-RCE and the increment in hematocrit during the RCE. We evaluated short-term complications of the magnitude and increments of hematocrit during RCE but further studies could assess potential long term complications resulting from higher post-RCE hematocrit.