Change in HbA1c post-transfusion is correlated to pre-transfusion HbA1c result
Authors: Kroner Grace , Jones Andrew , Bena James , Morrison Shannon , Bakdash Suzanne , Colón-Franco Jessica , Reineks Edmunds 
Published: November 2023

Abstract
Hemoglobin A1c (HbA1c) results are used to diagnose and monitor patients with diabetes mellitus. As such, they have a direct impact on patient care and treatment decisions. While within the laboratory community, there is the assumption that recent red blood cell (RBC) transfusion would interfere with HbA1c measurement, there is limited published evidence regarding whether HbA1c results provide an accurate estimate of long term glycemic control in patients who have received a RBC transfusion. This retrospective laboratory information system record review aims to address this gap in the literature with a retrospective analysis of patient results. Retrospective data was obtained from the laboratory information system. The study population included all patients over 18 years of age, both inpatients and outpatients, who had at least one HbA1c result during the study period (January 2018 – December 2020), and record of a RBC transfusion in the three months prior to the A1c result. Data collected included relevant laboratory results and transfusion information. 1,752 pre- and post-transfusion HbA1c pairs were analyzed. The average age of patients at transfusion was 66.0 years. Men comprised 51.7% of subjects (n=905). Most patients were White (64.0%; n=1,104), with Black (29.7%; n=513) and Multiracial / Multicultural (4.1%; n=71) subjects making up the largest minority. Most patients had diagnoses of anemia (93.0%; n=1,629) and/or diabetes (86.2%; n=1,511), with a minority having a diagnosis of any type of cancer (40.6%; n=712). Rarely, patients had hemoglobin disorders (3.1%; n=54). Most patients were treated with some form of glycemic control medication (91.5%; n=1,603). Average pre-transfusion HbA1c for all subjects was 7.0% ± 1.9 (1 sd). Average post-transfusion HbA1c for all subjects was 6.3% ± 1.3 (1 sd). The average change in HbA1c from pre- to post-transfusion was -0.7% ± 1.5 (1 sd). In contrast, the mean change in the random blood glucose measurement closest to the pre- or post-transfusion HbA1c was only -11.5 mg/dL (CI: -16.7 mg/dL to -6.2 mg/dL; p&lt;0.001). The median time between the pre-transfusion HbA1c and transfusion was 20.0 days; the median time between transfusion and the post-transfusion HbA1c was 38.0 days. There was a larger decrease in pre- to post-transfusion HbA1c in patients with diabetes (p&lt;0.001), patients without anemia (p=0.040), patients without hemoglobin disorders (p=0.045), patients without cancer (p=0.005), and patients on any glycemic control medication (p&lt;0.001). Overall, pre-transfusion HbA1c level was strongly associated with post-transfusion HbA1c level, with the greatest degree of negative change seen in patients with a pre-transfusion value &gt; 9.0%. In contrast, patients with a pre-transfusion value of &lt; 5.7% saw an average increase in HbA1c (p&lt;0.001). This study provides insight into the influence of transfusion on HbA1c results and reinforces the important role that pre-analytical factors play in laboratory testing.