DDKT Medical: The Kidney Transplant Process Explained

Deceased donor kidney transplantation, commonly abbreviated DDKT, is a surgical procedure in which a kidney from someone who has died is transplanted into a person with end-stage kidney disease. It remains the most common pathway to transplantation worldwide, and for most recipients it offers a meaningful survival advantage over staying on dialysis, with gains ranging from about six months to more than three additional years of life depending on age and existing health conditions.¹ The process involves far more than surgery day itself, stretching from a rigorous pre-transplant evaluation through organ preservation, immunological matching, the operation, and years of follow-up care.

Evaluation and the Transplant Waitlist

Before a person can receive a deceased donor kidney, they undergo an extensive medical workup. Transplant centers assess kidney function, screen for active infections and malignancies, and evaluate whether the candidate can tolerate major surgery and lifelong immunosuppression. One of the most critical parts of this evaluation is cardiovascular screening. People with advanced kidney disease carry elevated heart risk, and that risk climbs the longer they wait. In one single-center study, about a quarter of waitlisted patients experienced a major adverse cardiovascular event over a median follow-up of roughly five years, and the presence of significant coronary artery disease on angiography was the strongest predictor.²

Cardiovascular risk does not hold still while someone waits. A longitudinal study of waitlisted candidates found that roughly 27% started at a high cardiovascular risk level, and that figure climbed to over half after five years. Higher comorbidity burden was a consistent driver of worsening risk, and psychosocial distress was also a significant predictor.³ This is one reason transplant teams push for transplantation as early as feasible rather than treating the waitlist as a passive queue.

How Deceased Donor Kidneys Are Classified

Not all deceased donor kidneys are alike. The two main categories are donation after brain death (DBD), where the donor has been declared brain dead but the heart continues beating during organ recovery, and donation after circulatory death (DCD), where the heart has stopped and organs are recovered afterward. DBD has historically been the dominant source, but DCD programs have expanded steadily as transplant systems work to close the gap between organ supply and demand.

DCD kidneys come with a known trade-off. Because these organs experience a period of warm ischemia after circulatory arrest, recipients face about double the rate of delayed graft function, meaning the kidney does not work immediately and the patient needs dialysis in the first week after transplant. A large meta-analysis found the risk of delayed graft function was roughly twice as high in DCD recipients compared to DBD recipients, and the risk of primary nonfunction (where the kidney never works at all) was also elevated.⁴ However, the same meta-analysis showed that by ten years, graft survival was comparable between DCD and DBD recipients. Individual center data tells a consistent story: DCD kidneys have a rougher start, with longer hospital stays and more early biopsies, but they catch up to DBD kidney function within a couple of months and show similar medium-term graft survival.⁵

Each deceased donor kidney also receives a Kidney Donor Profile Index (KDPI) score, a percentile ranking that estimates quality based on donor age, height, weight, ethnicity, cause of death, and other factors. A KDPI of 20% means the kidney is estimated to be better than 80% of recovered kidneys. Higher KDPI kidneys come from older or sicker donors and have shorter expected graft survival. Among the highest-KDPI kidneys (98–100%), five-year allograft survival runs around 52%, compared to about 58% for kidneys in the 85–97% range.⁶ Even those numbers, however, often represent a net benefit over remaining on dialysis, particularly for older recipients with significant comorbidities.⁷

Immunological Matching and Allocation

Before a kidney is offered to a candidate, the transplant system checks for immunological compatibility. The key proteins involved are human leukocyte antigens (HLA), which sit on the surface of the donor kidney’s cells. If the recipient’s immune system recognizes these proteins as foreign, it can mount an attack that damages the graft. Better HLA matching between donor and recipient has been associated with better graft survival over decades of transplant data, though the strength of that association has weakened in modern eras as immunosuppressive drugs have improved.⁸

Another critical piece of the matching puzzle is whether the recipient has preformed antibodies against the donor’s HLA types. These are measured by panel reactive antibody (PRA) testing. Recipients who are “sensitized,” meaning they have high PRA levels due to prior transplants, blood transfusions, or pregnancies, face a harder time finding a compatible kidney. When PRA levels are high and the recipient carries antibodies targeting the specific donor’s HLA types, rejection rates climb and graft survival falls.⁹ Modern solid-phase immunoassays can detect these donor-specific antibodies with far greater sensitivity than older cell-based methods, and the development of new donor-specific antibodies after transplant is itself a warning sign for worse outcomes.¹⁰

Preserving the Organ Between Recovery and Transplant

Once a kidney is recovered from the donor, the clock starts ticking. Cold ischemia time, the period between when the organ is cooled and when blood flow is restored in the recipient, is one of the most important modifiable risk factors in deceased donor transplantation. Each additional hour of cold ischemia raises the risk of delayed graft function and graft failure.¹¹ In a large cohort study, the rate of delayed graft function rose steadily with cold ischemia time, from about 21% in the shortest-time group up to 36% in the longest, and primary nonfunction showed a similar trend.¹² The effect is especially pronounced for DCD kidneys, which already carry warm ischemia damage. For DCD organs, stretching cold ischemia beyond 12 hours significantly raises the hazard of graft failure at five years compared to DBD kidneys stored for the same duration.¹³

Traditionally, kidneys have been preserved by simple static cold storage: the organ is flushed with a cold preservation solution and packed on ice. An alternative is hypothermic machine perfusion, where the kidney is connected to a device that continuously pumps cold preservation fluid through it. A landmark trial in the New England Journal of Medicine demonstrated that machine perfusion cut the odds of delayed graft function by about 43% and was associated with better one-year allograft survival (94% versus 90%).¹⁴ A Cochrane systematic review confirmed these findings with high-certainty evidence, showing machine perfusion reduced the risk of delayed graft function for both DCD and DBD kidneys.¹⁵ A large registry-based analysis using propensity matching similarly found delayed graft function rates of about 21% with machine perfusion versus 29% with cold storage.¹⁶

The Transplant Surgery

The actual surgical procedure places the new kidney in the lower abdomen, usually in the iliac fossa. The surgeon connects the donor kidney’s artery and vein to the recipient’s iliac vessels, establishing blood flow. Then the donor ureter is implanted into the bladder to create a pathway for urine drainage. The recipient’s own kidneys are typically left in place unless they are causing problems such as recurrent infection or uncontrollable high blood pressure.¹⁷

A ureteral stent, a small tube placed inside the ureter at the time of surgery, is now routinely used at most centers. The stent supports the new connection between the ureter and bladder while it heals, and evidence suggests it reduces the rate of major ureteric complications such as leaks and strictures. The stent is typically removed endoscopically a few weeks later.¹⁸ One comparison of stent types found that internal double-J stents were associated with fewer urinary tract infections in the first six months than external stents, with a comparable rate of urological complications requiring intervention.¹⁹

Early Complications After Surgery

About a quarter of recipients experience at least one surgical complication in the first 30 days. The most common are fluid collections around the graft, particularly hematomas, followed by surgical site issues, urological problems like ureteral strictures, and vascular complications such as renal artery or vein thrombosis.²⁰

Among the most feared early events is renal vein thrombosis. Though rare, occurring in fewer than 2% of transplants, it carries a grim prognosis when it occurs after the initial operation. A large French study spanning over two decades found that when vein thrombosis was detected intraoperatively, the graft could often be salvaged, but when it was discovered postoperatively, emergency surgery resulted in a functioning graft in only about 8% of cases. Many patients required removal of the transplanted kidney.²¹

Delayed graft function remains the single most common early complication. The kidney, stressed by ischemia during recovery and storage, may not produce urine right away, requiring the recipient to continue dialysis for days or sometimes weeks. Managing it involves careful attention to blood pressure and fluid status, avoidance of drugs that are toxic to recovering kidneys, and biopsy of the graft if there is concern about acute rejection happening simultaneously.²² Over the long term, recipients who experience delayed graft function tend to have somewhat lower graft function and survival than those whose kidneys work immediately.²³

Immunosuppression After Transplant

Every deceased donor kidney recipient needs lifelong immunosuppressive medication to prevent the immune system from rejecting the transplanted organ. The regimen typically starts with an intense “induction” phase at the time of transplant and then transitions to lower-dose “maintenance” therapy.

For induction, the two most common agents are antithymocyte globulin (ATG), which depletes T cells, and basiliximab, which blocks a specific receptor on T cells. A meta-analysis of trials comparing the two found no significant differences in biopsy-proven rejection, graft loss, or patient death, but basiliximab was associated with a lower rate of infections and a lower rate of neoplasms.²⁴ That said, individual trials have found that ATG reduces the rate of acute rejection episodes more than basiliximab, though at the cost of more infections overall.²⁵ In practice, many centers reserve ATG for higher-risk patients, such as those who are highly sensitized, and use basiliximab for standard-risk recipients.

Maintenance immunosuppression most commonly involves a calcineurin inhibitor (usually tacrolimus) combined with an antiproliferative agent (usually mycophenolate mofetil), often with low-dose steroids. This combination was first introduced in the mid-1990s and has since been evaluated in numerous trials with varying protocols and doses.²⁶ The balancing act is always the same: too little immunosuppression risks rejection, while too much increases the likelihood of infections, diabetes, and certain cancers.

Rejection and How It Is Managed

Even with modern immunosuppression, some degree of immune attack on the graft remains a possibility. The two broad categories are T cell-mediated rejection, driven by immune cells directly attacking the graft, and antibody-mediated rejection, where antibodies target the donor’s HLA proteins. Tissue biopsy remains the gold standard for diagnosing rejection, and the histologic criteria for what counts as rejection have been refined considerably over the years.²⁷

T cell-mediated rejection is typically treated with high-dose intravenous steroids, with T cell-depleting agents reserved for steroid-resistant cases. Most episodes respond well to treatment. Antibody-mediated rejection is harder to reverse and is treated with plasma exchange and intravenous immunoglobulin, sometimes with the addition of rituximab. It remains one of the leading causes of late graft loss.

Viral Infections That Threaten the Graft

Immunosuppression opens the door to opportunistic infections that a healthy immune system would normally keep in check. Two viruses are particularly relevant to kidney transplant recipients: cytomegalovirus (CMV) and BK virus (BKV). Both can reactivate from latency when T cell immunity is suppressed, and both have well-documented negative effects on short- and long-term graft survival.²⁸

BK virus can cause a condition called BK virus-associated nephropathy, which directly damages the transplanted kidney. Patients who develop this nephropathy also appear more prone to CMV co-infection; in one study, about 39% of patients with BK nephropathy had concurrent CMV infection compared to 19% of patients without it.²⁹ The primary management strategy for both viruses involves reduction of immunosuppression to allow the patient’s own immune system to regain control, supplemented by antiviral medications for CMV. Because T cell recovery is central to fighting these viruses, there is growing research interest in adoptive virus-specific T cell therapy as a more targeted approach.

Long-Term Health After Transplant

Surviving the first year is a significant milestone, but DDKT recipients face a distinct set of long-term health challenges, many of them driven by the very medications keeping the graft alive. Post-transplant diabetes mellitus (PTDM) affects a substantial minority of recipients, with one study finding a rate of about 27% among kidney transplant patients over an average follow-up of nearly ten years.³⁰ PTDM is recognized as an important cardiovascular risk factor after transplant.³¹ In one retrospective cohort, the incidence of cardiovascular events was about 15% in patients who developed PTDM, compared to 6% in those who did not develop diabetes after transplant.³²

The transplanted kidney itself undergoes gradual wear. A process called interstitial fibrosis and tubular atrophy, sometimes abbreviated IF/TA, represents the slow scarring of kidney tissue. It is driven by chronic inflammation, activation of fibroblasts in the kidney, and buildup of scar-forming proteins, and it is one of the major pathways through which grafts eventually lose function over years and decades.³³ Many factors contribute, including prior episodes of rejection, chronic calcineurin inhibitor exposure, and recurrent infections. Slowing this process is one of the central goals of long-term transplant management.

The Survival Advantage of Transplant Over Dialysis

For all its complexity and risks, DDKT generally provides a clear survival benefit over staying on dialysis. A modeling study found that transplanting a waitlisted candidate, even one with comorbidities, gained between six months and more than three additional years of life compared to remaining on dialysis, at a cost-effectiveness ratio that fell well within standard thresholds.¹ Somewhat counterintuitively, the relative benefit is often greatest for higher-risk patients, those who are older or who carry more comorbidities. While their absolute survival is shorter than that of younger, healthier recipients, the gap between what transplant offers them and what dialysis offers them is actually wider. This is an important nuance for candidates who worry that their age or health conditions might make transplantation not “worth it.”⁷

Normothermic Machine Perfusion and Expanding the Donor Pool

One of the most active areas of research in deceased donor transplantation is normothermic machine perfusion (NMP), which keeps the kidney at body temperature and supplies it with oxygenated blood or a blood-based solution during the preservation period. The idea is that a warm, metabolically active kidney can be assessed in real time for quality, potentially allowing transplant teams to rescue kidneys that would otherwise be discarded.

Early clinical results have been mixed regarding whether NMP reduces delayed graft function compared to cold storage. A randomized trial of DCD kidneys found no difference in delayed graft function rates between a short period of NMP at the end of cold storage and cold storage alone, though the technique was shown to be safe and feasible.³⁴ Where NMP may have its biggest impact is not in improving outcomes for kidneys that would already be transplanted, but in salvaging kidneys that would otherwise be thrown away. A proof-of-concept study used NMP to assess DCD kidneys that had been declined by all centers due to poor flushing during recovery. After perfusion at body temperature, some of these kidneys were deemed viable. Five were transplanted successfully, and four had immediate graft function.³⁵ Preliminary work has also explored NMP for kidneys from donors with acute kidney injury at the time of death, with encouraging early safety data.³⁶

Kidneys From Very Young Donors

An uncommon but important scenario involves kidneys from very small pediatric donors. A kidney from an infant or toddler is much smaller than an adult kidney, so transplanting a single pediatric kidney into an adult recipient risks inadequate function. To address this, surgeons can transplant both kidneys together as a single unit, a technique called en bloc transplantation.³⁷

Outcomes with this approach are encouraging. A registry study from Australia and New Zealand found that en bloc and single pediatric donor kidney transplants had comparable graft survival, with ten-year death-censored graft survival of 91% for en bloc versus 87% for single kidneys. Median graft survival in the en bloc group exceeded 23 years.³⁸ A single-center comparison similarly found comparable five-year graft and patient survival between en bloc and single pediatric donor transplants, with the en bloc group trending toward lower rates of delayed graft function and acute rejection.³⁹ These pediatric donor kidneys grow after transplantation to match the recipient’s body, and their long graft survival makes them a valuable resource despite the technical complexity of the surgery.

Why Medication Adherence Matters So Much

The success of a kidney transplant over years and decades depends heavily on the recipient’s ability and willingness to take immunosuppressive medications consistently. Missing doses or reducing medications without medical guidance allows the immune system to mount a response against the graft, potentially leading to chronic rejection. In pediatric recipients, research has identified several psychosocial factors tied to poorer adherence, including elevated parental stress, problematic parent-child interactions, child behavioral issues, and dissatisfaction with physical appearance, which can be affected by medication side effects like weight gain or facial changes.⁴⁰ These findings underscore why transplant programs increasingly screen for psychosocial risk factors before and after transplant, and why patient and family support is treated as a medical priority rather than an afterthought.