One of the most familiar measurements in transplantation and organ preservation is cold ischemia time (CIT). It appears in organ offers, allocation discussions, clinical research, preservation decisions, quality reviews, and transplant outcome models. It is commonly treated as a simple number: how long was the organ cold?
But that question may be less straightforward than it appears.
After cross-clamp stops circulation, an organ can move through several distinct phases: cold perfusion, continued recovery in the donor, organ removal, back-table preparation, preservation-solution exposure, packaging, static cold storage, machine perfusion, transportation, implantation, and finally reperfusion. Different organs from the same donor may also move through those phases on very different timelines.
As transplantation increasingly incorporates broader geographic sharing, machine perfusion, donation after circulatory determination of death (DCD), and more complex logistics, it is worth asking a more fundamental question: when we report cold ischemia time, what exactly are we measuring?
Even the Definition of Cold Ischemia Time in Organ Preservation Is Not Uniform
The Organ Donation and Transplantation Alliance explicitly acknowledges this problem. Its DCD Educational Guide notes that no standardized definition of cold ischemic time exists and, for purposes of that guide, adopts the Organ Procurement and Transplantation Network (OPTN) definition: the amount of time an organ spends in preservation after recovery from the donor (The Alliance, 2025).
The Alliance glossary also describes cold ischemia time as the period an organ spends cold and without circulation, from removal from the donor until transplantation, while noting that you can also describe cold ischemia in relation to chilling and the later restoration of blood supply (The Alliance, 2026).
A recent international consensus uses a different starting point. In the 2026 Bucharest European Society for Organ Transplantation (ESOT) consensus, the authors defined cold ischemia time in controlled donation after circulatory determination of death (cDCDD) as the period between the start of cold perfusion of an organ and the restoration of its blood supply (Martin et al., 2026).
The definitions describe related concepts, but their starting points are not necessarily identical. Cold perfusion is not the same event as organ removal. Organ removal is not the same event as packaging. Packaging is not necessarily the beginning of every subsequent preservation strategy. The distinction matters because a single reported duration may combine several biologically and operationally different organ preservation phases.
What Is Cold Ischemia Time in Organ Preservation?
Cold ischemia time is the period an organ spends cold and without blood circulation during organ preservation. Under the OPTN definition, you measure the time an organ spends preserved after its recovery from the donor. Other definitions start the clock at cold perfusion, so you should confirm which event your data uses.
One Cross-Clamp Can Lead to Several Different Organ Preservation Timelines
In a multiorgan donor, several organs may share the same aortic cross-clamp event, but their experiences quickly diverge. Solid organ transplant recovery occurs in a deliberate sequence, and each organ enters its preservation and transportation pathway at a different point.
Kidneys are a useful example. Osband and colleagues described kidney "extraction time" as the interval beginning with aortic cross-clamp and perfusion/cooling and ending with kidney removal and placement on ice at the back table. In 576 deceased-donor kidneys, extraction time ranged from 14 to 123 minutes. The authors noted that kidneys routinely rank among the last solid organs that surgical teams remove during multivisceral procurement, and they linked each additional recovered organ to an average increase of 6.24 minutes in kidney extraction time (Osband et al., 2016).
Recent ESOT consensus work on cDCDD with normothermic regional perfusion (NRP) also illustrates why teams must explicitly consider organ-specific recovery sequence. For simultaneous thoracic and abdominal recovery, the consensus recommendations specify a sequence in which the team recovers the heart first, followed by the liver, lungs, and remaining abdominal organs, with liver recovery preceding pancreas and kidneys (Miñambres et al., 2026). The recommendation is specific to that clinical context, but it demonstrates a broader point: organ type changes the recovery timeline.
A heart, lung, liver, and kidney recovered from the same donor can therefore share a cross-clamp timestamp while entering definitive preservation, packaging, and transport at very different times. A common starting event does not create a common organ preservation exposure, even when the reported cold ischemia time looks similar.
Cross-Clamp Is Not the Same Thing as Cold Storage
The distinction becomes especially important when a timestamp is used as a surrogate for biology. Cross-clamp marks interruption of native circulation, but it does not necessarily mark the instant an organ reaches a uniform temperature, enters a defined organ preservation environment, or begins machine perfusion. As a result, cross-clamp can be an imperfect anchor for cold ischemia time.
In the kidney extraction-time study, Osband and colleagues proposed that the interval between cross-clamp and removal may represent an additional ischemic exposure because kidneys can rewarm while remaining in situ. Up to 60 minutes of extraction time was not associated with higher delayed graft function in their adjusted model, but beyond 60 minutes, each additional five minutes was associated with increased odds of delayed graft function. The authors also cautioned that time may be an imperfect surrogate for actual organ temperature (Osband et al., 2016).
The conceptual distinction is important. An organ is experiencing temperature, perfusion, oxygen availability, metabolism, preservation chemistry, and mechanical handling, not simply elapsed minutes on a clock.
Organ Type Changes the Meaning of Cold Ischemia Time
The phrase "cold ischemia time" can imply that the same clock has the same meaning for every organ. In practice, organ-specific recovery sequence, preservation limits, recipient-center logistics, and organ preservation technology create different timelines.
Thoracic organs and liver are generally recovered earlier than kidneys during multiorgan procurement, while kidneys may remain in the donor until other solid organs have been removed. Kidney back-table work, biopsy, packaging, static cold storage, and machine perfusion may then add additional phases before transportation or transplantation. The exact sequence varies by donor, organs recovered, clinical protocol, and local practice (Osband et al., 2016; Miñambres et al., 2026).
None of this means one organ is being "treated better" than another. It means the operational pathway is organ-specific. The same term should therefore be interpreted cautiously when it compresses different recovery and preservation pathways into one duration.
Cold Organ Preservation Is Biologically Active
The word "cold" can also create the impression that organ preservation simply pauses biology. Hypothermia markedly reduces metabolic demand, but it does not eliminate biological activity.
Experimental data illustrate this principle. In a 2025 porcine lung-transplant model, progressively longer periods of static cold storage produced time-dependent changes in multiple metabolites before reperfusion, and reperfusion produced additional metabolic shifts (Liang et al., 2025). The study used a lung model and should not be directly extrapolated to clinical kidney transplantation, but it reinforces the broader biological point that cold preservation is an exposure, not merely elapsed time.
If preservation conditions differ during the reported cold ischemia time, equal durations may not represent equal biological exposures.
Static Cold Storage and Machine Perfusion Complicate the Meaning of Cold Ischemia Time
Modern organ preservation adds another layer, especially as programs turn to machine perfusion to optimize kidney placement success. An organ may spend its preservation interval entirely in static cold storage, entirely in an organ perfusion and preservation strategy, or in sequential periods of static storage and machine perfusion. All of these phases can occur while an organ remains cold and without physiologic blood circulation, but they are not equivalent preservation environments.
Kidney data make the distinction particularly clear. Adani and colleagues studied kidneys that underwent a preliminary period of static cold storage followed by delayed hypothermic machine perfusion (HMP). The researchers linked longer static cold storage to higher vascular resistance and lower arterial flow at the beginning of machine perfusion. During HMP, resistance decreased and flow increased (Adani et al., 2020).
A large contemporary registry analysis similarly linked HMP to a lower adjusted risk of delayed graft function compared with static cold storage, including in a paired-kidney analysis of kidneys from the same donor (Li et al., 2025).
Machine perfusion also generates dynamic physiologic data. Jochmans and colleagues measured renal resistance at multiple points during HMP and found an independent association between terminal resistance and both delayed graft function and 1-year graft failure, although resistance alone had limited predictive accuracy (Jochmans et al., 2011). The implication is not that conventional CIT is unimportant. It is that two organs with the same reported cold ischemia time may have experienced very different preservation histories.
Operational Variation Shapes Organ Preservation Too
Organ preservation does not occur in isolation from logistics. Organ procurement organizations (OPOs) coordinate recovery, biopsy, pumping, allocation, and transportation across different clinical environments. A national survey of OPO practices found substantial variation in pumping practices and reported barriers related to staffing and transportation, while respondents also described growing challenges with organ transplant transportation under broader allocation (Concepcion et al., 2023).
Operational differences like these do not by themselves prove that a preservation interval is biologically different. They do show why a recorded cold ischemia time can be influenced by more than organ biology alone. Workflow, recovery sequence, staffing, transportation, and preservation strategy can all affect what occurs between two recorded events.
DCD Shows Why Precise Cold Ischemia Time Definitions Matter
Donation after circulatory determination of death provides a useful model for how transplantation can address this problem. Rather than describing the entire donation pathway with one broad ischemic interval, the 2026 Bucharest ESOT consensus defined a series of specific events and intervals, including the agonal phase, circulatory arrest, the acirculatory phase, total warm ischemia time, functional warm ischemia time, initiation of cold perfusion or normothermic regional perfusion, and cold ischemia time (Martin et al., 2026).
The purpose was not merely semantic. The consensus authors identified heterogeneity in terminology as a barrier to comparing protocols and outcomes, and emphasized that shared definitions are needed to harmonize data, facilitate research, and support meaningful comparisons between programs (Martin et al., 2026).
The same principle deserves consideration across organ preservation more broadly. If we want to understand what happens after cross-clamp, it may not be enough to know only the final duration assigned to "cold ischemia time."
Perhaps Organ Preservation Needs a Timeline, Not Just a Time
Cold ischemia time will remain an important transplant metric. It is simple and familiar, and research repeatedly links it to clinically relevant outcomes. Even so, a registry review of deceased-donor kidneys found that delayed graft function rose with CIT. Yet donor kidney quality had a stronger influence on graft outcomes in that same review. Increasingly sophisticated organ preservation strategies, such as kidney normothermic machine perfusion, may require more precise descriptions of CIT intervals.
A preservation timeline could distinguish cross-clamp, initiation of cold perfusion, organ recovery, and entry into a defined preservation environment. It could also mark packaging, static cold storage, machine perfusion, implantation, and reperfusion.
Not every organ would require every timestamp, and the goal should not be documentation for documentation's sake. The goal should be to identify which milestones represent meaningful changes in the organ's biological and preservation environment. The distinction may become increasingly important when comparing organ types, preservation technologies, procurement practices, programs, and transplant outcomes.
Better Organ Preservation Definitions Could Produce Better Data
The transplantation community already collects a large amount of timing information. Standardizing documentation for long-distance organ transportation is part of that effort. The challenge is making sure timestamps represent the same events when you compare them. The Alliance's Terminology & Data References resource supports that goal (The Alliance, 2026b). It aims to clarify commonly used terms and data definitions in donation and transplantation.
The problem goes beyond terminology. Suppose teams understand the start and end points of a cold ischemia time interval differently. You might then attribute differences to donor characteristics, procurement practice, preservation technology, or transplant outcomes. Yet part of that variation may reflect differences in what each program actually measured.
More precise organ preservation definitions could improve clinical research and registry analyses. They could also improve comparisons between preservation strategies, quality-improvement work, and the evaluation of new technologies.
Before We Ask How Long, We Should Ask What the Clock Measures
Cold ischemia time remains valuable. But the next evolution in organ preservation may not be simply finding ways to make one reported duration shorter. It may be understanding the preservation timeline with greater precision.
Before comparing a six-hour organ with a ten-hour organ, or deciding whether one preservation strategy performs better than another, three questions deserve attention: When did the clock start? What preservation conditions did the organ experience while the clock was running? And does the reported interval mean the same thing for every organ and every program?
The answers may ultimately tell us more than the number alone.
If your team is rethinking how organ perfusion and preservation milestones are tracked, reach out to Gold Standard Preservation to start the conversation.