How do kidney transplants work? - Alexander H. Toledo

In the 1930s, doctors began experimenting with a procedure long thought to be medically impossible: an organ transplant. Many pioneering surgeons focused on the kidney, taking a healthy one from a living or recently deceased person and transplanting it into a patient dying from kidney failure. But these early surgeries faced a major problem: patients’ immune systems would quickly recognize the new kidney as a foreign object and start to destroy it. Few patients survived past the first few days.

Then, in 1954, Joseph Murray attempted a type of kidney swap that no doctor had tried before. The surgery was a success, and the patient would go on to live the next 8 years with the transplanted organ, thanks to one key factor: it came from his identical twin. 70 years later, upwards of 100,000 kidneys are transplanted annually in the US alone.

So how does this surgery work today? Kidneys are true workhorses—these fist-sized organs filter the equivalent of an entire bathtub’s worth of blood each day. In addition to removing this waste and extra fluid through urine, the kidneys also regulate the production of red blood cells, vitamin D, and other hormones. Certain medical conditions can prompt the kidneys to work overtime, leading to gradual deterioration.

For example, in diabetes, higher blood sugar concentrations can trigger increased kidney filtration, swelling, and inflammation. High blood pressure can constrict and damage the organ’s delicate blood vessels. Over time, people can lose complete function of their kidneys and must rely on a treatment called dialysis to survive. Yet dialysis is time-consuming and fraught with serious medical complications. A kidney transplant offers a more permanent solution with a dramatically improved quality of life.

Once a patient is approved for the surgery, the search for a suitable organ begins. Historically, the biggest barrier was finding a donor whose immune system makeup closely resembled that of the patient’s, like an identical twin, as to reduce the risk of organ rejection. But today, thanks to medical advances, a patient’s family member, friend, or even a stranger can donate one of their kidneys. New drug therapies can effectively suppress a patient’s immune response before and long after the transplant, meaning that patients and donor pairs no longer must be perfect matches. Still, the closer the match, the better.

So another option is a paired organ exchange, where two or more incompatible donor and patient pairs are matched up, allowing each patient to receive a more compatible kidney from the other pair. Once an organ is found, the surgery itself is straightforward. First, the living donor's kidney is removed using minimally invasive and often robotic techniques. As for the transplant patient, an incision is made in their lower abdomen and the donor organ is implanted.

The new kidney’s artery and vein are connected to the recipient’s to create blood flow, and its ureter is attached to the patient's bladder. The failed kidneys are typically left in place, allowing them to continue to aid in filtration. After surgery, a patient is closely monitored for the next several days to ensure the new kidney starts filtering their blood, and subsequently producing urine on its own. This new kidney typically lasts between 12 to 20 years. Some people will have multiple kidney transplants in their lifetime, meaning at some point they may have four or even five kidneys in their bodies.

As for donors, most leave the hospital the next day, and can resume normal activity within a few weeks. While all surgeries carry risks, most donors go on to lead normal, healthy lives, facing no, or relatively few, complications related to living with a single kidney. But not all patients will have a willing living donor. In the US alone, around 90,000 patients sit on the national waiting list to be matched with a kidney from a deceased donor.

While many people register as organ donors, only 0.3% will lose their lives in circumstances that allow for organ donation. Due to this organ shortage, about 17 patients die every day waiting for a new kidney. Thankfully, doctors continue to push against the limits of what's possible, exploring new treatments and the potential of lab-grown, 3D printed, and even artificial kidneys.