When Compatibility Creates Inequality: Blood Type O and the Korean Heart Transplant System

Organ transplantation has always walked a fine line between clinical urgency and logistical feasibility, with blood type compatibility serving as one of the immutable variables in allocation. In this issue of the Korean Circulation Journal, Kim et al.¹⁾ present a compelling and timely analysis of heart transplant outcomes in Korea across ABO blood types, highlighting a profound and persistent inequity affecting type O recipients.

Using a comprehensive national registry of 1,745 heart transplant cases over a 13-year period, the authors reveal that type O patients, despite constituting over one-third of the donor pool, experience the longest waiting times (median 110 days) and the highest mortality (78.1%) on the transplant waitlist. This disparity arises from their unique role as universal donors but restricted recipients—a paradox inadequately addressed by current allocation protocols in Korea.

Importantly, this study provides the first nationwide data in Korea quantifying the clinical disadvantage experienced by blood type O patients under the existing heart allocation framework. Although, the post-operative 10-year survival rates were 63.1% for blood type A, 66.1% for B, 63.3% for AB, and 67.1% for O, with no statistically significant difference among the groups (p=0.208), the disproportionate pre-transplant burden borne by type O patients raises serious concerns about fairness and systemic inefficiencies.

The authors highlight potential areas for improvement in Korea’s allocation policy, specifically regarding blood group-based matching, in light of approaches adopted in other countries. For instance, in the United States, the United Network for Organ Sharing (UNOS) policy mandates prioritization of type O organs for type O and B recipients. However, following the 2018 revision of the U.S. allocation system, type O candidates have undergone heart transplantation less frequently and have experienced higher rates of waitlist mortality or clinical deterioration. The proportion of type O hearts allocated to secondary ABO candidates increased significantly (from 12.0% to 14.5%) under the new system. Furthermore, type O candidates are more likely to require left ventricular assist device implantation and be listed at status 3 or lower.²⁾ This phenomenon closely mirrors the challenges observed in Korea’s heart allocation system (Figure 1).

Figure 1. Inequity in organ allocation: challenges for blood type O recipients in Korea.

This figure illustrates the systemic disadvantage faced by blood type O recipients in organ transplantation in Korea. Although blood type O donors have a broad donation scope—able to donate to recipients with blood types A, B, AB, and O—significant proportion (38%) of their organs are allocated to non-O recipients.¹⁾ This wide distribution leads to a relative donor shortage for type O recipients. As a result, O-type patients experience longer waiting times and often require bridging therapies such as LVADs. However, once stabilized on LVAD, these patients may receive a downgraded urgency status, further delaying transplantation. Collectively, these factors contribute to higher waitlist mortality among blood type O recipients, highlighting an inequity in organ allocation driven by blood type compatibility.

LVAD = left ventricular assist device.

Eurotransplant applies ABO blood group rules variably across member countries. In high-urgency heart-only transplants, Eurotransplant follows a specific ABO compatibility approach. Type A recipients can only receive from type A donors; type AB recipients can receive from all blood types except type O; type B recipients can receive from type B and O donors; and type O recipients can only receive from type O donors.³⁾ The French allocation system is similar: blood type A donor hearts are allocated to type A and AB candidates; type O grafts only to type O and B candidates; and type B grafts to type B and AB candidates.⁴⁾

In Korea, donor selection for heart transplantation follows this sequence: 1) single-organ transplants prioritized by urgency; 2) recipients in the same region with identical blood type; 3) recipients in a different region with identical blood type; 4) recipients in the same region with compatible blood types; and 5) recipients in a different region with compatible blood types.⁵⁾ This structure provides only minimal protection for type O recipients. For instance, if no type O recipients are listed as status 0 when a donor becomes available, type A, B, or AB recipients with status 0 are prioritized over type O recipients with lower urgency status (status 1, 2 or 3). Given that approximately 40–50% of heart transplants in Korea involve patients on extracorporeal membrane oxygenation (ECMO) support,⁶⁾,⁷⁾ and that non-type O blood groups are frequently listed among high-urgency candidates, the likelihood of type O patients status 1–3⁸⁾ receiving donor hearts diminishes further.

As we move toward more transparent, equitable, and outcome-driven organ allocation systems, this study underscores a critical point: equity does not always result from neutrality. Rather, it often requires intentional efforts to correct structural imbalances. For policymakers, transplant coordinators, and clinicians, the message is clear—blood type should not be the principal determinant of waitlist mortality. Nevertheless, it is important to recognize that prioritizing patients in critical condition, such as those requiring ECMO, regardless of blood type, may be considered ethically justifiable. Therefore, any revisions to the allocation system must be approached with careful consideration and balanced judgment.