Donor mobilization during U.S. mass casualty and disaster events: Differential effects on whole blood and apheresis platelet supply

Abstract

Background

Mass casualty and disaster events (MCEs) and national blood donation appeals generate surges in blood donation, but how these responses differ by product type, donor demographics, and retention remains incompletely understood, particularly for apheresis platelets.

Study Design and Methods

We analyzed donation data from five major U.S. MCEs and five national blood donation appeals between 2000 and 2024, characterizing whole blood (WB) and platelet donations by donor age, first‐time versus repeat status, and return within 1 year.

Results

WB donation demonstrated rapid, high‐amplitude surges during MCEs that resolved within 1–2 weeks, driven in part by younger and first‐time donors. In contrast, appeals produced smaller increases sustained through the duration of the appeal. Platelet donation followed a distinct pattern, with a smaller, yet slightly longer surge response during MCEs and more robust increases during national blood donation appeals, while both relied almost exclusively on older, repeat donors. Donor retention differed primarily by donor history. Repeat donors were substantially more likely to return than first‐time donors across age groups and event types, with older repeat donors showing the highest retention.

Discussion

These findings highlight structural differences between WB and platelet donor systems with direct implications for disaster preparedness and long‐term blood supply resilience in the United States.

Abbreviations

ARC

American Red Cross

CI

confidence interval

CIs

confidence intervals

LCL

lower confidence limit

MCE

mass casualty of disaster event

MCEs

mass casualty or disaster events

OR

odds ratio

ORs

odds ratios

PLT

platelet

SAS

statistical analysis software

SQL

structured query language

SWD

standardized weekly donation

SWDs

standardized weekly donations

UCL

upper confidence limit

WB

whole blood

1. INTRODUCTION

Disasters and mass casualty events (MCE), defined here as acute incidents that place sudden stress on health care systems and blood collection operations, place sudden and unpredictable stress on the blood supply. ¹ , ² , ³ , ⁴ , ⁵ In the wake of such events, public altruism often translates into surges in blood donation, sometimes overwhelming collection sites with first‐time donors eager to help. ⁶ , ⁷ , ⁸ , ⁹ The extraordinary response following September 11, 2001, the Boston Marathon bombing, hurricanes, and mass shootings illustrates the willingness of communities to act in moments of crisis. ⁷ , ¹⁰ , ¹¹ However, these surges do not always mirror actual transfusion demand and may also contribute to product wastage. Yet despite the visibility of these events, relatively little is known about the composition of the donor populations mobilized or their long‐term contribution to the blood system.

Blood donations spike during disasters, but patterns are not uniform across donation type. ⁷ , ¹⁰ Whole blood (WB) donation is simple, widely accessible, and frequently the entry point for first‐time donors. ¹² In contrast, apheresis platelet donation requires specialized equipment, extended procedure times, and higher levels of donor commitment, making it more reliant on experienced repeat donors. ¹³ , ¹⁴ This distinction is particularly consequential in the United States, where approximately 97% of the platelet supply is collected by apheresis rather than from WB‐derived platelets. ¹⁵ As a result, understanding apheresis donor behavior during crises is central to platelet supply preparedness.

Similarly, while it is often assumed that disasters bring forward large numbers of new donors, the durability of this mobilization remains poorly characterized. Prior reports suggest that first‐time donors are important for short‐term supply augmentation but often do not become repeat participants. ¹¹ , ¹⁶ Without systematic analysis, however, the blood community lacks a clear understanding of whether crisis‐driven donation translates into longer‐term donor engagement and blood supply sustainability. ⁶

These differences in donor accessibility and commitment are particularly important in the context of disaster response. Whole blood collection programs can accommodate large numbers of new donors more readily, but retention remains the challenge. Apheresis platelet donation, by contrast, has historically depended on a smaller, highly committed donor base. ¹⁷ If this base is insufficiently responsive during crises or becomes increasingly fragile as donors age, the ability to maintain platelet supply during disasters could be compromised. To date, no published study has comprehensively examined platelet donor mobilization in this setting.

Prior work on disaster‐related blood donation has largely focused on operational outcomes, such as meeting immediate patient needs, managing surges at collection sites, or avoiding product wastage. ⁷ , ⁸ , ¹⁰ , ¹¹ , ¹⁶ Few studies have characterized the types of donors who respond, how their participation differs by product type, or whether they remain engaged after the event has passed. This represents a critical gap, as the long‐term resilience of the blood system depends not only on meeting immediate needs but also on strengthening the donor pool and surge supply for future crises.

The present study addresses this gap by analyzing donation data from 10 events. We examined five U.S. mass casualty or disaster events, including September 11, Hurricane Sandy, the Boston Marathon bombing, Hurricane Harvey, and the Las Vegas shooting, along with five national blood donation appeals issued when blood availability reached critically low levels. The objectives of this retrospective national analysis were threefold: first, to compare the temporal patterns of whole blood (WB) and apheresis platelet donation surrounding mass casualty or disaster events and national blood donation appeals; second, to characterize donor composition by age and first‐time versus repeat donor status; and third, to evaluate return to donate within 1 year after event‐related donation. In addition, we propose a conceptual model of donor mobilization to integrate these findings and highlight implications for preparedness.

By clarifying which types of donors are mobilized during disasters, how long their participation lasts, and how platelet donors contribute, this work provides a more complete understanding of the strengths and vulnerabilities of the blood system. These insights are critical for developing strategies that not only meet immediate needs but also enhance long‐term donor retention and system resilience.

Accordingly, we designed the study to evaluate differences in temporal response, donor composition, and post‐event return across product type and event category. MCE windows were selected to capture the total observed ARC donor response surrounding each event, whereas national appeals were analyzed as planned mobilization efforts.

2. STUDY DESIGN AND METHODS

2.1. Data source and extraction

Donation data were obtained from the ARC national donor database, which captures donor demographics, donation history, product type, and donation dates for all ARC collections. All data were de‐identified prior to analysis. Data extraction and storage were conducted in accordance with institutional data governance, privacy, and security standards using Teradata SQL (v.17.20).

2.2. Event selection and study design

We conducted a retrospective observational cohort study to analyze blood donation patterns surrounding five MCEs and five national blood donation appeals between 2000 and 2024. For the purposes of this study, MCEs were defined operationally as discrete disasters or violent events that place abrupt stress on health care systems and blood collection operations. The MCE analyses were intended to capture the overall observed donor response at a national level during the defined peri‐event window surrounding each incident, whereas the national appeals were analyzed as a separate category representing planned blood‐supply‐driven mobilization. Events and appeals were selected based on their scale, anticipated transfusion demand, and disruption to routine blood collection operations. Appeal wording, targeting strategy, and collection modality were not analyzed and may influence product‐specific response. Although Figure 1 depicts donation patterns for a single representative national appeal, all analyses of donor demographics, mobilization, and retention incorporate pooled data from the five national appeals included in the study (September 2021, January 2022, April 2023, September 2023, and January 2024).

FIGURE 1.

(A) Weekly whole blood (WB) donations across major U.S. events. Donation counts are also standardized to each event (Standardized Weekly Donations, SWD). Left y‐axis line graphs show the total weekly whole blood collections during specific events with the baseline data for a few weeks prior to each event (4‐week moving average) as baseline. Right y‐axis light‐red bar‐graphs indicate the standardized values for these total weekly donations. Z‐score standardization was implemented, using the formula (weekly donation − average weekly donation 4 weeks before and after the incident)/(standard deviation). Standardized values indicate how many standard deviations the weekly donations are from the means of a data set for each incident/appeal. For example, countrywide whole blood collection during the week of September 11 (2001w37) were 3 standard deviations greater than the average collection between weeks 28 through 46. Collections returned to baseline levels about 4 weeks later after the disaster. X‐axis represents the year and week for these incidents. WB donations show sharp, short‐term surges. (B) Weekly platelet donations across mass casualty or disaster events and a planned appeal. Donation counts are also standardized to event baselines (Standardized Weekly Donations, SWD). Left y‐axis line graphs show the total weekly platelet collections during specific events with the baseline data for a few weeks prior to each event (4‐week moving average) as baseline. Right y‐axis light‐red bar‐graphs indicate the standardized values for these total weekly donations. Standardized values indicate how many standard deviations the total weekly donations are from the means of a data set for each event. X‐axis represents the year and week for these events. Platelet donation increases were more gradual and sustained over longer periods compared to WB donations represented in Figure 1A.

Although the duration of blood donation appeals may vary in response to blood demand and collection levels, a standardized analytic window was defined to ensure comparability across appeals. Donation data were systematically analyzed from 4 weeks before the start of each appeal through 4 weeks after its conclusion. This pre‐ and post‐appeal interval served as a common baseline reference window for standardization rather than a modeled explanation for why each appeal was initiated. In practice, however, appeals commonly follow substantial supply declines associated with seasonal respiratory illness, inclement winter weather, busy holiday schedules, reduced new donor participation, staffing challenges, and fewer blood drives at schools and businesses. This design allowed comparison of both the magnitude and duration of donation surges relative to baseline activity.

2.3. Donation characteristics and standardization

Donations were categorized by product type (WB vs. apheresis platelets), donor age, and donor history (first‐time vs. repeat). First‐time donors were defined as individuals with no prior recorded donation at the index event‐related donation, whereas repeat donors had a prior recorded donation before the index donation. Weekly donation volumes were calculated for each event and stratified by donor history and product type.

To enable comparison across events with differing baseline volumes, donation activity was normalized using standardized weekly donations (SWD). SWD were calculated as Z scores using the mean and standard deviation of weekly donation counts pre‐event and post‐event: SWD = (x_i − μ)/σ, where x_i was the donation count during the specific week, μ was the average of weekly donations pre‐ and post event, and σ was the standard deviation of weekly donations pre‐ and post‐event. Standardization was performed separately for first‐time and repeat donors because these groups differ in baseline donation frequency and regularity. Because this approach standardizes variation within each event window rather than against an exclusively pre‐event baseline, SWD values should be interpreted as relative deviations within each event rather than causal estimates of change from baseline

2.4. Retention analysis

Donor retention was defined as any subsequent donation occurring within 1 year of the incident‐related donation. Retention analyses were restricted to donors eligible to return within that interval and were stratified by donor type, age group, product, and event category. Return within 1 year was used as a pragmatic proxy for early sustained donor engagement.

2.5. Statistical analysis

Mixed effects regression model for repeated measures to determine differences in donation volume before and after an event or appeal: Donation trends were summarized descriptively and visualized by event and product type. A mixed‐effects regression model was used to estimate differences in total donations across weeks during any event while accounting for clustering and repeated measurements. The outcome variable was standardized weekly donations. SWD was calculated using the mean and standard deviation of weekly donations during the defined peri‐event analytic window. Because this approach standardizes variation within each event window rather than against an exclusively pre‐event baseline, SWD values should be interpreted as relative deviations within each event rather than causal estimates of change from baseline. The primary determinant was phase (weeks before vs. after an event or appeal start, with week 0 representing the event week or appeal start week), with first‐time donation status included as a fixed covariate. To address temporal correlation arising from repeated weekly observations, the week/year of donation was modeled as a repeated measure, with the covariance structure allowed to vary by phase. Adjusted least‐squares means were estimated for each phase, and pairwise comparisons between phases were conducted to assess differences in donation volume across the events or appeals timeline. All tests were two‐sided, and statistical significance was assessed using an α level of .05. These analyses were performed using SAS 9.4 (SAS Institute, Cary, NC).

2.6. Logistic regression to determine odds of returning based on donation history and donor age

The primary outcome was return to donate, defined as a binary indicator (returned vs. did not return). Predictor variables included donor type (first‐time or returning at the index donation) and age group. An interaction term between donor type and age group was included to evaluate whether the association between donor type and return behavior varied across age categories.

A logistic regression model was fitted with a logit link to estimate odds ratios (ORs) and 95% confidence intervals (CIs). These analyses were performed using R statistical software (R Foundation for Statistical Computing).

3. RESULTS

3.1. Temporal patterns of donation following mass casualty or disaster events and appeals

Whole blood donation demonstrated pronounced, event‐specific surges following MCEs (Figure 1A). Across all MCEs, WB collections increased abruptly, peaking during the incident week, and returned to baseline within approximately 1–2 weeks. The largest increase occurred following September 11, 2001, when WB collections reached SWDs above baseline. Other MCEs produced similarly sharp but short‐lived increases, with peak SWD values ranging from 2.3 to 2.4. In contrast, national blood donation appeals were associated with smaller increases in WB donation that were sustained through the time period in which the appeal was maintained (Figure 1A). Peak WB collections typically occurred several weeks after appeal initiation and remained elevated until the appeal was stopped. These differences in surge timing were consistent across other appeals evaluated.

Platelet donation followed a distinct temporal profile (Figure 1B). During MCEs, platelet collections increased modestly, generally reaching 1–2 SWD (Figure S1) above baseline and returned to baseline within weeks. In contrast, appeals were associated with more sustained elevations in platelet donation, with peaks occurring later than those observed during MCEs and persisting for several weeks.

Analysis of estimated mean SWDs using mixed‐effects models (Figure S1) demonstrated an overall increase in both WB and platelet donations during the week of a MCE and during the weeks following an appeal compared with preceding weeks. For both products, surges during MCEs peaked in the incident week, whereas surges associated with appeals peaked later and were more sustained. Importantly, these temporal patterns were similar for first‐time and repeat donors, indicating that differences in surge magnitude and duration were driven primarily by event type rather than donor history.

Together, these findings demonstrate that WB donation is characterized by rapid, high‐amplitude mobilization during acute events, whereas platelet donation shows a smaller observed surge response during MCEs and greater sensitivity to planned recruitment efforts, with consistent patterns observed across donor types.

3.2. Donor age and donor‐type composition differs by product

Donor composition differed markedly by product type with respect to both age and donor history (Figure 2). Platelet donation was overwhelmingly sustained by repeat donors, with 99.4% of platelet units collected from repeat donors during mass casualty or disaster events (MCEs) and appeals. In contrast, whole blood (WB) donation included a substantially larger contribution from first‐time donors. During routine collections, first‐time donors account for 15.4% of WB donations, increasing to approximately 21% during MCEs and appeals.

FIGURE 2.

Age distribution of donors by product type (Platelets [PLT] vs. Whole Blood [WB]) across all events and appeals combined showing age‐related differences in product‐specific donation behavior. Younger donors (<29 years) predominantly donate whole blood (27.4%), whereas platelet donation is concentrated among older donors (≥55 years: 53.4%). Middle‐aged donors (30–55 years) show similar representation for both products. Data pooled across all events and appeals.

Age distributions further distinguished WB and platelet donor populations. More than 92% of platelet units were donated by individuals aged ≥30 years, with donors aged ≥55 years contributing 53.4% of all platelet donations. Donors younger than 29 years accounted for only 7.9% of platelet units. In contrast, WB donation was more evenly distributed across age groups: 27.4% of WB units were donated by individuals younger than 29 years, 41.4% by donors aged 30–55 years, and 31.2% by donors aged ≥55 years.

Incident‐related mobilization altered donor composition for WB but not for platelets. During MCEs and appeals, the proportion of first‐time WB donors increased across all age groups, with approximately 6% absolute increases among younger (<29 years) and middle‐aged (30–55 years) donors and a smaller increase (2–3%) among older donors (≥55 years). In contrast, platelet donation remained almost exclusively dependent on repeat donors across all age strata and event types, with no meaningful influx of first‐time donors.

3.3. Event‐specific donor mobilization patterns by age and donor history

Figure 3 illustrates that event‐related surges reflect selective mobilization of specific donor subgroups rather than uniform increases across the donor pool. During both MCEs and appeals, increases in total donations reflected differential mobilization of specific donor subgroups rather than uniform increases across the donor pool.

FIGURE 3.

Weekly blood donation counts (log scale) before and during/after blood donation appeals and mass casualty or disaster events (MCEs), stratified by donor status (first‐time vs. repeat) and age group. Repeat donors accounted for higher donation volumes across all age groups. Appeals and MCEs were associated with increased donations, with the largest relative increases among younger repeat donors during appeals (+2.2%) or MCE (+3.3%), and middle‐aged first‐time donors during MCE (+4.2%). The highest absolute volumes were from repeat donors aged 30–55 years during MCEs; however, their relative change during MCE vs. regular donation events was minimal (0.1%). Percentages indicate the proportion of donors within specific categories grouped by time before and after the events, with negative values representing pre‐event weeks and positive values representing post‐event weeks.

Among repeat donors, younger donors (<29 years) demonstrated increased participation during both appeals and MCEs. During appeals, the proportion of young repeat donors increased from 10.2% to 12.4%, whereas during MCEs it increased from 20.0% to 23.4%. Middle‐aged repeat donors (30–55 years) showed smaller relative shifts.

First‐time donor mobilization was most pronounced among middle‐aged donors during MCEs. The proportion of first‐time donors aged 30–55 years increased from 33.8% during routine collections to 36.2% following MCEs. Younger first‐time donors contributed substantially to absolute WB donation volumes during events; however, their proportional representation among all donors did not increase compared with routine collections, indicating that surges in younger first‐time donors reflected overall volume expansion rather than preferential recruitment.

In contrast, platelet donation exhibited minimal variation in donor composition across events. Platelet collections remained dominated by older, repeat donors, with no meaningful shifts in age or first‐time donor participation during either MCEs or appeals. These findings indicate that platelet mobilization during events reflects increased activity within an existing donor base rather than recruitment of new or younger donors.

3.4. Donor return behavior by age, donor history, and event type

Donor return within 1 year differed substantially by donor history and age (Figure 4 and Table 1). Across all age groups and both product types, repeat donors were significantly more likely to return than first‐time donors. Retention was consistently higher following appeals than following MCEs.

FIGURE 4.

Return rates between first‐time and repeat donors. Percentage of first‐time and repeat donors returning to donate within 1 year after initial donation during a mass casualty or disaster event, MCE (top panel) and a planned appeal (bottom panel), stratified by age group. Repeat donors consistently exhibited higher return rates than first‐time donors across all age groups and contexts. Retention was substantially greater following appeals compared to MCEs, with the highest return observed among repeat donors aged ≥55 years (73%). Differences between first‐time and repeat donors were statistically significant (p < .05).

TABLE 1.

Odds ratios for return within 1 year by donor age group and donor history.

Differences of age group vs. donor type odds ratio for return within a year of donation
Age, donor	Vs. comparison group	Odds ratio	LCL	UCL
55–, Repeat donor	−29, First‐time donor	8.24	8.18	8.30
55–, Repeat donor	55‐, First‐time donor	6.52	6.43	6.60
55–, Repeat donor	−29, Repeat donor	4.60	4.57	4.63
30–55, Repeat donor	30–55, First‐time donor	4.47	4.44	4.50
30–55, Repeat donor	−29, First‐time donor	4.09	4.06	4.12
30–55, Repeat donor	55‐, First‐time donor	3.23	3.19	3.27
30–55, Repeat donor	−29, Repeat donor	2.28	2.27	2.30
−29, Repeat donor	−29, First‐time donor	1.79	1.78	1.80
55–, First‐time donor	−29, First‐time donor	1.27	1.25	1.28

Note: The table compares the likelihood of donor return within a year across combinations of donor age and first‐time versus repeat donor status. Older repeat donors had the highest odds of return, with 55+ repeat donors showing more than eightfold higher odds of returning compared with younger first‐time donors. Across all comparisons, repeat donors consistently demonstrated substantially greater retention than first‐time donors.

Among repeat donors, return rates increased with age, reaching 73% among donors aged ≥55 years. Repeat donors aged 30–55 years had return rates of 63%, whereas repeat donors younger than 29 years returned at a rate of 49% (Figure 4). In contrast, first‐time donors demonstrated uniformly low return rates across age groups. Following appeals, first‐time donor return rates were approximately 11% for donors younger than 29 years and 30–55 years, and 13% for donors aged ≥55 years, with even lower rates observed following MCEs.

Multivariable analysis confirmed donor history as the strongest predictor of return (Table 1). Older repeat donors had more than eightfold higher odds of returning compared with younger first‐time donors (odds ratio, 8.24; 95% CI, 8.18–8.30). Although older age modestly increased the likelihood of return among first‐time donors, donor history remained the dominant determinant of sustained donation behavior.

3.5. Summary of observed donor system behavior

Collectively, these data demonstrate that event‐driven donation surges are supported by distinct donor subpopulations. WB donation surges reflect mobilization of younger and first‐time donors, with measurable shifts in donor composition during MCEs and appeals. Platelet donation, in contrast, relies on an older, repeat‐donor base with limited compositional change during events. Retention analyses further indicate that sustained participation is driven primarily by repeat donors, particularly older individuals, regardless of product type.

4. DISCUSSION

In this large, national analysis spanning more than two decades, we demonstrate that disaster‐driven blood donation is supported by two distinct donor ecosystems whose mobilization dynamics, demographic composition, and retention potential differ in predictable and consequential ways. These findings provide a systems‐level framework for understanding blood supply resilience during crises.

First, we show that WB and platelet donors respond differently to acute disasters and planned appeals. MCEs trigger rapid, high‐amplitude surges in WB donation that resolve quickly, whereas platelet donation shows a smaller and more transient observed surge response. Planned appeals, by contrast, support more sustained increases (dependent on how long the appeal is issued) in both WB and platelet donations, particularly for platelets. These findings highlight that platelet mobilization, albeit smaller, is more sustained compared to WB during MCEs and likely reflects multiple factors: the logistical demands of apheresis collection and distribution, and the more structured outreach to established platelet donors.^10,15,19,20

Second, donor demographic analyses reveal that WB and platelet donation depend on fundamentally different populations. WB donation draws from a broad, flexible donor base, including younger and first‐time donors who can be rapidly mobilized during crises. Platelet donation, however, relies disproportionately on an older, highly committed repeat donor cohort with lower capacity for rapid expansion. This demographic concentration likely contributes to lower surge capacity in the apheresis platelet system and may represent a structural vulnerability for platelet supply, particularly as donor populations age and platelet demand continues to increase.

Third, retention analyses demonstrate that donor history is the primary determinant of sustained participation. Although first‐time donors contribute meaningfully to acute WB surges, particularly during MCEs, their likelihood of returning is low. Repeat donors, especially those in older age groups, exhibit the highest retention across all contexts. These findings indicate that crisis altruism, while effective for short‐term supply augmentation, does not reliably translate into durable donor engagement without intentional follow‐up strategies.

These results expand on previous reports on blood donor response and supply risks during crisis events. ⁷ , ⁸ , ¹⁰ , ¹¹ , ¹⁶ , ¹⁷ , ¹⁸ Collectively, these results underscore the need for preparedness strategies that explicitly acknowledge the dual nature of the donor ecosystem. Reliance on episodic WB surges cannot ensure long‐term resilience, particularly for platelet supply. Planned appeals, structured re‐contact of established apheresis donors, targeted retention efforts, and deliberate recruitment of younger platelet donors will be necessary to sustain blood availability in both routine operations and future crises. In addition, broader implementation of WB‐derived pooled platelets may provide a complementary strategy to strengthen platelet surge resilience, and production of WB‐derived pooled platelets is currently being planned.

Strengths of this study include its scale, national scope, and inclusion of platelet donation behavior, an area largely absent from prior disaster‐response literature. Limitations include reliance on data from a single national blood provider, the use of return within 1 year as a proxy for long‐term retention, the absence of regional analyses, and the fact that appeal wording, product‐specific targeting, and collection modality were not modeled. Future work should examine regional variability, longer‐term donation trajectories, and how appeal content influences product‐specific response.

In conclusion, disaster‐driven blood donation reflects two interdependent but structurally distinct donor systems. Recognizing and addressing the unique constraints of each will be essential for translating crisis responsiveness into durable blood supply resilience.

FUNDING INFORMATION

This study received no external funding. This work was supported solely by institutional resources.

CONFLICT OF INTEREST STATEMENT

The authors have disclosed no conflicts of interest.

Supporting information

FIGURE S1. Estimated standardized weekly donations (SWD) for whole blood (A, B) and platelets (C, D) in the weeks surrounding mass casualty or disaster events (MCEs) and blood donation appeals, stratified by donor status (first‐time vs. repeat). Values represent model‐based marginal means from mixed‐effects models from 5 weeks before through 5 weeks after the event or appeal start (vertical reference line). Appeals were associated with larger and more sustained increases in SWD than MCEs, with higher post‐event contributions among repeat donors across blood product types.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.