Characterizing red blood cell age exposure in massive transfusion therapy: the scalar age of blood index (SBI)

Abstract

Background: The mortality of trauma patients requiring massive transfusion to treat hemorrhagic shock approaches 17% at 24 hours and 26% at 30 days. The use of stored RBCs is limited to less than 42 days, so older RBCs are delivered first to rapidly bleeding trauma patients. Patients who receive a greater quantity of older RBCs may have a higher risk for mortality.

Methods and materials: Characterizing blood age exposure requires accounting for the age of each RBC unit and the quantity of transfused units. To address this challenge, a novel Scalar Age of Blood Index (SBI) that represents the relative distribution of RBCs received is introduced and applied to a secondary analysis of the Pragmatic, Randomized Optimal Platelet and Plasma Ratios (PROPPR) randomized controlled trial (NCT01545232, https://ichgcp.net/clinical-trials-registry/NCT01545232). The effect of the SBI is assessed on the primary PROPPR outcome, 24-hour and 30-day mortality.

Results: The distributions of blood storage ages successfully maps to a parameter (SBI) that fully defines the blood age curve for each patient. SBI was a significant predictor of 24-hour and 30-day mortality in an adjusted model that had strong predictive ability (odds ratio, 1.15 [1.01-1.29], p = 0.029, C-statistic, 0.81; odds ratio, 1.14 [1.02-1.28], p = 0.019, C-statistic, 0.88, respectively).

Conclusion: SBI is a simple scalar metric of blood age that accounts for the relative distribution of RBCs among age categories. Transfusion of older RBCs is associated with 24-hour and 30-day mortality, after adjustment for total units and clinical covariates.

Conflict of interest statement

Conflicts of Interest

The authors, SD, DB, AJ, JMY, JFP, RP, CW, and JH, declare that they have no conflicts of interest relevant to the manuscript submitted to TRANSFUSION.

HW provides research consultation for Shire, Inc.

© 2019 AABB.

Figures

FIGURE 1.

Graph of the cumulative scalar blood age index (SBI) for 5 representative patients from the PROPPR trial. The table shows these patients’ exact PRBC units and their predicted 24 hour and 30 day mortality from the model. For example, patient 1 received a total of 9 PRBC units: 8 were aged 0–7 days old and 1 was 8–14 days old. The inlaid table maps SBI to age categories and predicted mortality at 24 hours and 30-days. Note: The predicted mortality is calculated at the sample mean or median for the following adjusters in the model: patient age, sex, race, mechanism of injury, Injury Severity Score, Revised Trauma Score, total PRBC units transfused in the first 24 hours after admission, and PROPPR trial treatment group.

FIGURE 2:

Distribution of SBI among all PROPPR trial patients. Patients transfused with predominately younger RBCs have increasingly more negative SBI values; whereas, patients transfused with predominately older RBCs have increasingly higher positive SBI values.

FIGURE 3:

The (unadjusted) proportion of 24-hour and 30-day patient mortality by SBI tertile and total PRBC units received. Mortality proportions are given on the y-axis by both SBI tertile on the first x-axis, and total PRBC blood unit category on the second x- axis. This 3-dimensional plot shows how mortality in PROPPR changes as a function of both SBI and total number of blood units received.