Kidney Transplant - An Overview
Kidney transplantation is the renal replacement therapy of choice for those patients with end stage renal disease. When compared with either haemodialysis or peritoneal dialysis, transplantation confers major survival advantages as well as a better quality of life. In the UK, there are nearly 7,000 people waiting for a kidney transplant at any one time and approximately 2700 kidney transplants take place per year, with a third of those kidneys coming from live donors.
Roughly speaking, a kidney transplant provides about two thirds of the function of healthy native kidneys, whereas dialysis only provides about 5% of native function. A transplant provides the major advantage of giving freedom from dialysis and means that all fluid and dietary restrictions, essential to the renal patient on dialysis, become a thing of the past. Other advantages of successful transplantation include enabling patients to gain employment, giving higher energy levels and improvements in their sex lives and overall allowing a more fulfilling life. Women are also more likely to become pregnant and give birth to a healthy baby.
Which patients are eligible for a transplant?
Nearly half of all patients with renal failure are suitable for transplantation if a donor kidney is available to them. As observational studies suggest that patient survival after having a transplant is worse the longer a patient is on dialysis, pre-emptive transplantation is encouraged in most transplant centres. This means that the transplant takes place form 6 months before the patient would start dialysis.
Many units do not have an age limit for transplantation and each patient is individualized according to the risks and benefits involved. However an age of about 70y is the normal cut-off, but older patients can be transplanted depending on their clinical circumstances.
There are contraindications to kidney transplantation, some are absolute but others are relative. Examples of absolute contraindications include active malignancy, ongoing untreated infections, and irreversible cardiac, lung or peripheral vascular disease. Psychiatric illness, substance abuse and a known failure to comply with medication are examples of relative contraindications.
There are some primary renal diseases that potentially reoccur in the transplanted kidney. Examples are FSGS (focal segmental glomerulosclerosis) or IgA nephropathy. These need to be discussed carefully pre-transplantation but often are a greater problem associated with a second transplant. These diseases might contraindicate a further transplant.
Preparation for a transplant
The process of evaluation for a potential candidate for a transplant is multidisciplinary, and amongst others, involves transplant surgeons, nephrologists and transplant coordinators. The aims of this multidisciplinary assessment is to pick up any contraindications to transplantation, determine potential immunological problems and screen for comorbidity that needs to be managed before the transplant can take place. There are also social and psychological factors that need to be assessed.
Immunology; finding the right kidney.
Immunological evaluation starts with the identification of potential prior antigen exposure. This could have occurred from previous transplants, blood product transfusions and pregnancies. Testing of blood types and human leukocyte antigen (HLA) typing is carried out to detect both potential matches and conversely donor-recipient pairs that would not have a good immunological outcome.
Matching the blood group is more straightforward than matching the tissue type and follows certain principles, similar to blood transfusions (see table 1). In some transplant centres such as the West London Renal and Transplant Centre, sophisticated means by which blood group antibodies are removed pre-transplantation enables donor-recipient pairs with mismatched blood groups can still go ahead and donate a kidney. This is known as 'antibody incompatible transplantation'.
Group A or O
Group B or O
As there are so many possible tissue types, matching the donor tissue type to the recipient is highly complex. Essentially, the more of these tissue type characteristics that are similar in both donor and recipient, the higher the chance that the transplant kidney will work. Due to the large number of tissue types, it is rare to get an exact match. However if the patient and donor have three or more of the major HLA tissue type characteristics in common, the transplant will be offered. The matching of tissue type in living donors is slightly less important and so a less satisfactory match is acceptable for successful transplantation.
Live versus deceased donor kidney transplantation
A deceased donor transplant, (formerly known as a cadaveric donor), is the term used to describe an organ used for transplantation that has been retrieved from someone who has died. In this country about two thirds of kidneys transplanted come from these donors, most often who have died from intracerebral haemorrhages (a bleed into the brain) and are brain stem dead. A smaller number of organs are retrieved from patients who have died but who do not fulfil brain stem death criteria and have no hope of recovery. Life sustaining treatment is withdrawn, after which the organs are retrieved. This is referred to as donation after circulatory death. Due to the shortage of organs in this country a growing number of transplants are from this source. When a deceased donor organ becomes available, co-ordination within NHSBT (NHS Blood and Transplant) offers the organs out to recipients that are highest on the waiting list. Factors that would push a patient to the front of the list would include how close the tissue type is to the donor, blood type, age and age match, time on the waiting list etc. Ethnic minorities namely Afrocaribean and Asians tend to wait longer than Caucasians.
Live donation is when a relative or someone close to the patient with renal failure donates one of their kidneys. Kidneys from live donors have better long-term patency than deceased donor kidneys. There are other major benefits from living related transplantation. Waiting times tend to be shorter and this is particularly relevant in renal failure patients from ethnic minorities who can wait a while on the deceased donor renal transplant list. Also, unlike a deceased donor transplant, which is on an emergency basis with no prior warning, live donation is a planned elective procedure. Live donation is much more likely to allow for pre-emptive transplantation.
Live renal donation is increasing in its popularity and numbers as the procedure becomes more widely accepted. Risks to the donor are minimal and most renal units aim to perform as many as possible knowing that it confers the best results and due to the shortage of organs from deceased donors.
The surgical procedure
The incision for a kidney transplant is usually an oblique incision in the iliac fossa (lower abdomen, just above the groin). The renal vein is anastomosed (surgically sewn together) to the external iliac vein and the renal artery to the external iliac artery. (These blood vessels are those found above the groin level and supply blood to the legs). Often there are multiple vessels. The ureter is attached to the bladder – a ‘ureteroneocystostomy’. A ’jj’ stent is placed from the ureter to the bladder to help keep this anastomosis (connection) open and patent.
Complications of renal transplantation
In the early phase post transplantation, there are certain complications to be aware of. These include post-operative haemorrhage and vascular thrombosis (untoward clotting) that must be identified immediately. Delayed graft function (where the patient needs dialysis before the transplanted kidney starts to make urine) rejection and side effects of the long-term immunosuppressant regimen should all be recognized and the recipient must be counselled as to all these potential complications. Very careful follow-up after discharge, in the transplant clinic, continues for 12 months after transplantation after which the frequency of visits to the clinic is tailed off. GP management at this point is crucial; any changes in plasma creatinine (the measure of kidney function) and other aspects of renal function must be reported to the transplanting centre. Many units, such as the West London Renal and Transplant Centre at the Hammersmith Hospital have ‘walk-in’ rapid assessment units for renal and transplant patients.