Screening and medical management of feline kidney transplant candidates
Kidney transplantation is a viable therapeutic alternative for cats with end-stage renal failure. The first successful kidney transplantation in a cat was performed in 1987 at the University of California-Davis School of Veterinary Medicine.1 Veterinary surgeons at transplant centers across the country have since performed several hundred successful kidney allograft transplants in cats.
Not all patients with chronic kidney disease are good candidates for kidney transplantation, and postoperative care requires intense medical management. In this article, we review the indications, diagnostic evaluation, and complications of kidney transplantation in cats. We also briefly describe the medical and surgical management of these patients.
CHRONIC KIDNEY DISEASE: A COMMON CAUSE OF MORBIDITY AND MORTALITYChronic kidney disease is a progressive, irreversible condition that affects a large percentage of cats. It is among the most common diseases in older cats, with a reported prevalence of 1.6% to 20%.2,3 One study reported the prevalence of renal failure was 12% in all cats examined at a referral-based veterinary teaching hospital.4 In geriatric cats older than 15 years, the prevalence increased to slightly greater than 30%.
Chronic kidney disease is characterized by functional or structural injury that has resulted in irreversible histologic changes. Kidney function is evaluated by performing a complete blood count, a serum chemistry profile, a urinalysis, and diagnostic imaging. Changes in blood urea nitrogen and creatinine concentrations and possible abnormalities in serum phosphorus concentrations, other electrolyte concentrations, and hematocrit or packed cell volume (PCV) combined with decreased urine concentrating ability are commonly used to assess the severity and progression of disease.
Fortunately, the kidneys have a tremendous reserve capacity; however, this reserve can delay the diagnosis of acute or chronic kidney disease until marked damage has occurred. Inadequate urine concentrating ability is generally associated with a loss of two-thirds of functional nephrons, while a loss of three-fourths of functional nephrons results in azotemia. Cats may maintain some concentrating ability despite azotemia and, thus, may be in overt renal failure without isosthenuria. By the time renal dysfunction is detected by using standard clinicopathologic tests, clinicians must assume that kidney disease is severe. In some cats, kidney transplantation offers successful treatment.
HISTORY OF KIDNEY TRANSPLANTS
Organ transplantation was first attempted early in the 20th century, using animal models. Kidney allograft transplantation (organs from other individuals of the same species) was first described by Alexis Carrel, who pioneered many vascular surgical techniques still used today.5 Early transplants were technically successful, although the transplanted kidney allografts were inevitably rejected. It was not until the development of immunosuppressive drugs in the early 1960s that prolonged survival was achieved.6 Cyclosporine revolutionized kidney transplantation through its selective inhibition of T lymphocytes, the main cell type responsible for kidney allograft rejection.7,8
Kidney transplantation is the treatment of choice in many people with end-stage kidney disease. It is an attractive alternative to hemodialysis or long-term peritoneal dialysis since quality of life and survival are greater. The transplant patient mortality rate is less than 5% in the first year.9 This success rate is a reflection of extensive research in immunosuppressive therapy and recipient-donor matching. Live donor allografts remain superior to cadaveric grafts, but 60% of patients still receive grafts from human cadavers because of insufficient donor numbers.9
Over the last decade, organ transplantation in veterinary medicine has become more common. Corneal, bone marrow, and kidney grafts have all been successfully transplanted. Kidney allograft transplantation has been successful in both dogs and cats, although canine kidney transplantation presents a greater challenge because of the level of immunosuppression required to prevent allograft rejection.10,11 Rejection episodes in dogs are frequent and severe, and canine recipients require multiple-agent immunosuppressive protocols and intensive management.10,12 Several recent studies have explored triple-drug (cyclosporine, azathioprine, and prednisolone) protocols and histocompatibility matching with limited success; to date, high complication and mortality rates in dogs still preclude widespread use of kidney transplantation.12
However, kidney allograft transplantation in cats has become an accepted treatment for patients with end-stage kidney disease. In a study of 66 cats receiving kidney transplants at the University of California-Davis School of Veterinary Medicine, 71% of the cats survived until discharge.13 The one-year survival rate in this early case series was 51%, but advances in surgical technique have anecdotally resulted in greater survival times.14,15