Assessment of Average Hematocrit of Red Cell Units for Erythrocytapheresis Procedure in Sickle Cell Disease

Background:

Erythrocytapheresis, or red blood cell exchange (RCE) is a non-invasive procedure in which a patient's erythrocytes are removed from the bloodstream while being replaced with erythrocytes from blood donors. RCE is commonly used as a transfusion technique in patients with sickle cell disease (SCD) to help treat and prevent complications associated with sickling of erythrocytes and iron overload.

The AABB consensus report (1) outlines the procedural guidelines for RCE including appropriate indications and ideal forms of vascular access. However, the guidelines make no recommendation for determining the hematocrit (Hct) of the red cell bags for the procedure.

Institutions take several different approaches to determine how many red cell units to exchange. The number of units needed depends on the volume and Hct of the individual units as well as the patient's pre-procedure Hct and HbS levels, height, weight, and the desired HbS and Hct targets. Red cell units are routinely labeled with volume, but are not generally labeled with Hct. The AABB consensus report (1) states that some institutions use an estimated Hct of 56% to 57% for each unit. The report rationalizes the use of an estimated Hct for input for the RCE, by citing the approximated Hct of bags of red cells (55% to 60%) with additive solution produced from whole blood donation, based on limited data.

The goal of our study was to determine the average Hct on the red cell units used for RCE.

Methods:

This study used a retrospective chart review to investigate the Hct of red cell units during a RCE in a calendar year. Our institution uses pre-storage leuko-reduced red blood cells units in citrate phosphate dextrose adenine (CPDA-1) and adsol preservative (AS-1), which are 21 days old or less for RCE. The average Hct of the bags of red cells infused during the procedure was determined by accessing each bag for a small sample of blood to determine the Hct. Data was excluded if the patient did not meet standard weight requirements (> 30 kg) or required additional treatment protocols including the use of washed cells or machine priming.

Results:

A total of 297 encounters were recorded for 30 different patients. A total of 1953 bags (approximately 517 liters of red cell units in volume) were administered. Data from the encounters were used to calculate measures of central tendency. The average calculated Hct for each encounter was 63.3%, with a median and mode Hct being 63% and 62%. The range of Hct from the bags was 54.6% to 72.9%. The average Hct of the bags ranged from 60.6% (in March) to 64.8 % (in July).

Conclusions:

Our study suggests a higher average Hct of transfused red cell units than stated in the AABB consensus report (1), which was based on limited data. Our findings indicate that a standardized average of 63.3%, would be appropriate for our institution. Conversely, our findings also signify that the standardized average Hct must be determined in each institution prior to their application for RCE. However, our data also reveals that it is possible to subject patients to estimates as far as 9.7% above and 9.6 % below the true average Hct of the red cell bags used. The process of determination of Hct for each of the red cell units increases the time of pre-service activities, laboratory costs, and the overall infusion center time for the patients leading to higher costs per infusion. Consequently, using a standardized average of the Hct would result in cost savings. We have therefore adopted the practice of using the standardized average of Hct of 63.3% for RCE in our patients.

Reference:

1. Biller E, Zhao Y, Berg M, Boggio L, Capocelli KE, Fang DC, Koepsell S, Music-Aplenc L, Pham HP, Treml A, Weiss J, Wool G, Baron BW. Red blood cell exchange in patients with sickle cell disease-indications and management: a review and consensus report by the therapeutic apheresis subsection of the AABB. 2018 Aug;58(8):1965-1972. doi: 10.1111/trf.14806