Geographic distribution and acuity circles

Geographic distribution in U.S. organ allocation refers to the rules that determine where a deceased-donor organ is offered, that is, which candidates count as "close enough" to the donor to receive priority.[1][2] Over roughly two decades, the geographic basis of allocation has evolved through three broad stages: from fixed administrative units (the donation service area (DSA) and the OPTN region), to fixed-distance acuity circles measured in nautical miles from the donor hospital, and toward continuous distribution, which eliminates hard geographic boundaries and instead treats distance as one weighted factor in a Composite Allocation Score.[1][2][3]

This evolution was driven by the federal OPTN Final Rule (42 CFR §121.8), which directs that allocation policies "shall not be based on the candidate's place of residence or place of listing" except as required by medical judgment, and that organs be distributed "over as broad a geographic area as feasible" in order of decreasing medical urgency.[4] As of mid-2026, no organ system still uses the DSA or region as a primary allocation unit; liver, kidney, pancreas, heart, and lung all use distance-based or continuous frameworks.[1][2][3]

The historical units: DSA and OPTN region

For most of the modern era of U.S. transplantation, the first units of organ distribution were the donation service area and the OPTN region.[1][5] A DSA was the geographic territory served by a single organ procurement organization (OPO); there were 58 DSAs.[5] The 11 OPTN regions were larger groupings of DSAs used for the second tier of sharing.[5] Under this system, an organ was generally offered first to candidates within the donor's DSA, then within the region, then nationally, with candidates ranked by urgency within each geographic tier.[1][5]

The DSA-and-region system was increasingly criticized as arbitrary.[5][6] DSA boundaries had been drawn for OPO service-area purposes, not to reflect transplant need or travel time, and they produced inequities: an urgently ill candidate at a hospital just across a DSA or region boundary could be passed over in favor of a less-urgent candidate inside the boundary.[5][6] HHS directed the OPTN to reconsider the DSA as a first level of distribution, citing "the arbitrary nature of DSA boundaries" and the risk that urgent candidates near a donor might not receive priority because they were across an administrative line.[6] Litigation over geographic disparities, particularly in liver and lung allocation, accelerated the change.[1][6]

Acuity circles and fixed-distance allocation

The replacement framework offered organs within fixed distances (concentric circles) measured in nautical miles from the donor hospital, rather than within administrative units.[1][7] Because candidates are prioritized within these circles by medical urgency ("acuity"), the liver framework is commonly called acuity circles.[1][7] The circles are anchored on the donor hospital, so the relevant geography is the actual distance an organ would travel, addressing the boundary problem of the DSA system.[1][7] This change rolled out organ by organ:

• Lung (November 24, 2017). In an emergency change responding to an HHS directive and litigation, the OPTN removed the DSA as the first unit of lung distribution and began offering adult-donor lungs first to candidates within 250 nautical miles of the donor hospital; 250 nautical miles was selected to limit cold-ischemia time and transport cost.[8]
• Heart (October 18, 2018). The revised adult heart allocation status system likewise removed the DSA and made the most-local distribution level the candidates within 250 nautical miles of the donor hospital.[9]
• Liver and intestine (February 4, 2020). The OPTN replaced the 58 DSAs and 11 regions with acuity circles of 150, 250, and 500 nautical miles. The highest-urgency liver candidates (Status 1A/1B) are prioritized first within 500 nautical miles, then candidates are offered by descending severity, expanding outward through the 150-, 250-, and 500-nautical-mile circles.[7][10]
• Kidney and pancreas (March 15, 2021). The OPTN removed the DSA and region from kidney, pancreas, kidney-pancreas, and islet allocation, replacing them with a 250-nautical-mile circle from the donor hospital, supplemented by proximity points that add weighted priority based on how close a candidate's hospital is to the donor hospital.[11][12]

The proximity-points concept introduced with kidney and pancreas allocation was an important bridge toward continuous distribution: rather than a hard boundary, distance began to be expressed as graduated points, so that closer candidates received more priority without an absolute cutoff.[11][12]

Toward continuous distribution

Continuous distribution is the endpoint of this evolution.[2][3] It removes geographic boundaries entirely and folds distance into a single weighted Composite Allocation Score (CAS) alongside medical urgency, expected post-transplant survival, candidate biology, and patient access.[2][3] Under continuous distribution, no candidate is excluded by a boundary or admitted by one; instead, every candidate receives a score in which proximity contributes weighted points, and the match run ranks candidates continuously.[2][3]

Continuous distribution was implemented first for the lung, effective March 9, 2023, making lung the first organ to eliminate hard geographic boundaries in this way.[2][13] As of mid-2026, lung is the only organ live on continuous distribution; kidney, pancreas, liver, intestine, and heart remain on acuity-circle or distance-based frameworks while their continuous-distribution policies are developed and put to public comment.[3]

Regulatory basis

The driver of this evolution is 42 CFR §121.8 of the OPTN Final Rule.[4] Its key geography-related provisions are:[4]

• allocation policies "shall not be based on the candidate's place of residence or place of listing, except to the extent required" by the medical-judgment and best-use criteria (§121.8(a)(8)); and
• allocation policies shall be designed to achieve equitable allocation by, among other goals, "distributing organs over as broad a geographic area as feasible … and in order of decreasing medical urgency" (§121.8(b)(3)).

Together these provisions disfavor allocation defined by administrative residence/listing geography and favor distribution that is as broad as is medically and logistically feasible, which is the legal rationale for moving from the DSA and region first to acuity circles and then to continuous distribution.[1][4]

See also

• OPTN allocation policy
• Continuous distribution and the Composite Allocation Score
• The match run
• MELD / MELD-Na / MELD 3.0 (and PELD)
• Heart allocation status system
• Lung Allocation Score (LAS)
• Organ procurement organization (OPO)

References

• HRSA / OPTN. Continuous Distribution. https://www.hrsa.gov/optn/policies-bylaws/policy-issues/continuous-distribution
• UNOS / OPTN. New lung allocation policy in effect. https://unos.org/news/new-lung-allocation-policy-in-effect/
• HRSA / OPTN. Continuous distribution policy issues and per-organ status. https://optn.transplant.hrsa.gov/policies-bylaws/a-closer-look/continuous-distribution/
• 42 CFR §121.8, Allocation of organs (OPTN Final Rule). Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/cfr/text/42/121.8
• UNOS. New national liver and intestinal organ transplant system in effect Feb. 4, 2020 (replaces 58 DSAs / 11 regions). https://unos.org/news/new-national-liver-and-intestinal-organ-transplant-system-in-effect-feb-4-2020/
• HRSA / OPTN. Frequently asked questions about the removal of donation service area (DSA) and OPTN region from kidney, pancreas, and islet allocation. https://optn.transplant.hrsa.gov/professionals/by-organ/kidney-pancreas/frequently-asked-questions-about-the-removal-of-donation-service-area-dsa-and-optn-region-from-kidney-pancreas-kidney-pancreas-and-islet-allocation/
• UNOS. Pre-implementation notice: liver and intestinal organ distribution based on acuity circles (150/250/500 NM), Feb. 4, 2020. https://unos.org/news/pre-imp-notice-liver-intestinal-dist-acuity-circles-feb-4-2020/
• HRSA / OPTN. Policy modification to lung distribution sequence (250 nautical miles, Nov. 24, 2017). https://optn.transplant.hrsa.gov/news/policy-modification-to-lung-distribution-sequence/
• HRSA / OPTN. OPTN/UNOS Board approves revised adult heart allocation system (Oct. 18, 2018). https://optn.transplant.hrsa.gov/news/optnunos-board-approves-revised-adult-heart-allocation-system-clarifies-exception-points-for-liver-transplant-candidates-with-hepatocellular-carcinoma/
• Policy and oversight of cardiac transplantation (DSA elimination; nautical-mile boundaries). PMC12082465. https://pmc.ncbi.nlm.nih.gov/articles/PMC12082465/
• UNOS. March 15 policy implementation: removal of DSA from kidney and pancreas allocation (250-NM circle + proximity points). https://unos.org/news/mar-15-policy-implementation-remove-dsa-kidney-pancreas-allocation/
• HRSA / OPTN. New kidney, pancreas allocation policies in effect (March 15, 2021). https://optn.transplant.hrsa.gov/news/new-kidney-pancreas-allocation-policies-in-effect/
• HRSA / OPTN. New lung allocation policy in effect (continuous distribution effective March 9, 2023). https://www.hrsa.gov/optn/news-events/news/new-lung-allocation-policy-effect