Kidney Transplantation¶
Chapter 325 | Part 9: Disorders of the Kidney and Urinary Tract
KEY CLINICAL POINTS¶
- Kidney transplantation is the treatment of choice for end-stage kidney disease (ESKD), with >220,000 patients living with transplants in the U.S.
- 1-year survival rates for living-donor and deceased-donor allografts are 98% and 93%, respectively, but long-term graft survival remains suboptimal.
- The Kidney Donor Profile Index (KDPI) guides allocation, with KDPI <20% allocated to highest-risk recipients and >85% to lower-risk recipients.
- Immunosuppressive therapy (e.g., calcineurin inhibitors, mTOR inhibitors) is critical to prevent rejection, with newer agents like belatacept reducing CNI toxicity.
- Chronic complications include CNI nephrotoxicity, BK virus nephropathy, and hypertension, requiring regular monitoring and adjustment of immunosuppression.
1. DEFINITION & OVERVIEW¶
Kidney transplantation is the definitive treatment for ESKD. The first successful transplant occurred in 1954 between identical twins. Immunosuppressive therapies (e.g., azathioprine, prednisone) enabled allografts in nonidentical individuals. Modern outcomes include 1-year survival rates of 98% for living-donor and 93% for deceased-donor grafts, though long-term survival has not improved significantly.
Table 325-1: Non-Heart-Beating Donor (DCD) Definitions¶
| Category | Definition |
|---|---|
| I | Brought in dead |
| II | Unsuccessful resuscitation |
| III | Awaiting cardiac arrest |
| IV | Cardiac arrest after brainstem death |
| V | Cardiac arrest in a hospital patient |
1.1 Historical Milestones¶
First successful transplant in 1954; introduction of immunosuppressants in the 1960s; calcineurin inhibitors in the 1980s improved 1-year survival rates.
1.2 Organ Allocation¶
The 2014 UNOS allocation system prioritizes highly sensitized patients and allocates high-quality organs to those with the longest expected survival. KDPI scores guide allocation, with KDPI <20% allocated to highest-risk recipients.
2. EPIDEMIOLOGY¶
Global demand for kidneys exceeds supply, with ~139,000 candidates on the U.S. waiting list as of 2022. Deceased-donor transplants account for 70% of transplants, while living-donor transplants are associated with better short-term outcomes. Risk factors include obesity, diabetes, and racial disparities (e.g., African-American patients with blood type B face longer wait times).
Table 325-2: Graft and Patient Survival Rates (1999–2018)¶
| Donor Type | 1-Year | 5-Year | 10-Year |
|---|---|---|---|
| Deceased Donor | 94% | 76% | 54% |
| Living Donor | 98% | 87% | 70% |
2.1 Demographics¶
Age-related mortality peaks in the first year post-transplant (6.8% for ≥ 50–60 years). African-American patients with blood type B face longer wait times due to higher prevalence of B blood type in this population.
2.2 Donor Shortage¶
As of 2022, ~25,000 transplants occur annually in the U.S., but demand outstrips supply. Marginal donors (e.g., DCD, HIV-positive donors) are increasingly used to expand the donor pool.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Chronic allograft dysfunction results from a combination of alloimmune response, drug toxicity, and ischemia-reperfusion injury. Acute rejection involves T-cell-mediated (interstitial fibrosis, tubular atrophy) and antibody-mediated (C4d deposition, complement activation) mechanisms. Non-HLA antigens and eplet mismatches also contribute to rejection risk.
3.1 Rejection Mechanisms¶
T-cell-mediated rejection involves CD4+ and CD8+ T cells attacking donor HLA antigens. Antibody-mediated rejection is driven by donor-specific antibodies, with C4d deposition in peritubular capillaries as a diagnostic marker.
3.2 Genetic Factors¶
Non-HLA antigen polymorphisms (e.g., LIMS-1 locus) and eplet mismatches in HLA DQ loci are risk factors for acute rejection. TPMT genotyping is critical for azathioprine dosing.
4. CLINICAL FEATURES¶
Acute rejection presents with fever, tenderness, and rising creatinine. Chronic complications include CNI nephrotoxicity, BK virus nephropathy, and hypertension. Post-transplant lymphoproliferative disease (PTLD) and opportunistic infections (e.g., CMV, Pneumocystis jirovecii) are significant risks.
4.1 Acute Rejection¶
Typically presents with fever, tenderness, and rising creatinine. Diagnosis requires allograft biopsy and Banff classification. T-cell-mediated rejection shows interstitial infiltration; antibody-mediated rejection shows C4d deposition.
4.2 Chronic Complications¶
CNI nephrotoxicity, BK virus nephropathy, and hypertension are common. Chronic allograft dysfunction is associated with recurrent glomerular disease, fibrosis, and vascular changes.
5. DIFFERENTIAL DIAGNOSIS¶
Post-transplant dysfunction must differentiate between acute rejection, acute tubular necrosis, BK nephropathy, and prerenal azotemia. Infections (e.g., CMV, Pneumocystis) and drug toxicity (e.g., calcineurin inhibitors) must also be considered.
5.1 Functional vs. Structural Causes¶
Acute tubular injury (ATI) vs. rejection: ATI shows bland tubular epithelium; rejection shows interstitial inflammation. BK nephropathy presents with tubular cytopathic changes and viral antigens.
5.2 Infections¶
CMV, Pneumocystis, and BK virus are common opportunistic infections. Diagnostic tests include viral load, imaging, and allograft biopsy.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis involves crossmatching (cytotoxic and flow cytometric), HLA typing, and allograft biopsy. Noninvasive biomarkers (e.g., cell-free DNA, urine chemokines) are emerging for rejection detection. Imaging (ultrasound, CT) helps identify obstruction or thrombosis.
Table 325-3: Maintenance Immunosuppressive Drugs¶
| Agent | Pharmacology | Mechanisms | Side Effects |
|---|---|---|---|
| Glucocorticoids | Increased bioavailability with hypoalbuminemia and liver disease | Binds cytosolic receptors and heat shock proteins | Hypertension, glucose intolerance, dyslipidemia, osteoporosis |
| Cyclosporine | Lipid-soluble polypeptide | Trimolecular complex with cyclophilin and calcineurin | Nephrotoxicity, hypertension, dyslipidemia |
| Tacrolimus | Macrolide, well absorbed | Trimolecular complex with FKBP-12 and calcineurin | Diabetes, hirsutism |
| Mycophenolate | Metabolized to mycophenolic acid | Inhibits purine synthesis via inosine monophosphate dehydrogenase | Diarrhea, stomatitis |
| Belatacept | Fusion protein, intravenous injections | Binds CD80/CD86, prevents CD28 binding | Posttransplant lymphoproliferative disease |
6.1 Crossmatching¶
Cytotoxic crossmatch detects preformed anti-HLA antibodies. Flow cytometric crossmatch identifies anti-HLA IgG not detected by cytotoxic assays.
6.2 Allograft Biopsy¶
Gold standard for diagnosing rejection. Banff classification guides diagnosis of acute T-cell or antibody-mediated rejection.
7. MANAGEMENT & TREATMENT¶
Immunosuppressive therapy includes induction agents (e.g., ATG, basiliximab) and maintenance drugs (e.g., CNI, mTOR inhibitors). Acute rejection is treated with steroids, IVIG, or anti-CD20 antibodies. Chronic complications require dose adjustments, antiviral prophylaxis, and monitoring for BK virus.
Table 325-4: Opportunistic Infections in Transplant Recipients¶
| Time Period | Infections |
|---|---|
| Peritransplant (<1 month) | Wound infections, Herpesvirus, Oral candidiasis, Urinary tract infection |
| Early (1–6 months) | Pneumocystis carinii, Cytomegalovirus, Hepatitis B |
| Late (>6 months) | BK virus (polyoma), Herpes zoster, Hepatitis C |
7.1 Induction Therapy¶
Antithymocyte globulin (ATG) is used for high-risk patients. Basiliximab is preferred for low-risk patients. Belatacept reduces CNI use and toxicity.
7.2 Maintenance Therapy¶
CNI (cyclosporine, tacrolimus) and mTOR inhibitors (sirolimus, everolimus) are first-line. Belatacept is an alternative to CNI. Monitoring drug levels and interactions is critical.
8. PROGNOSIS & COMPLICATIONS¶
1-year survival is excellent, but long-term graft survival is ~12–19 years for deceased and living donors, respectively. Major causes of death include cardiovascular events (29%), infections (18%), and malignancy (17%). Chronic complications include CNI nephrotoxicity, BK virus, and hypertension.
8.1 Long-Term Outcomes¶
Average allograft survival is 19 years for living donors and 12 years for deceased donors. Chronic allograft dysfunction is driven by recurrent glomerular disease, fibrosis, and vascular changes.
8.2 Malignancy Risk¶
Incidence of tumors is 5–6% in transplant recipients, 100x higher than the general population. Skin cancers and posttransplant lymphoproliferative disease are most common.
9. SPECIAL CONSIDERATIONS¶
Pregnancy requires careful immunosuppression adjustment to avoid fetal complications. Pediatric recipients need growth monitoring and dose adjustments. Elderly patients face higher surgical risks. HIV-positive donors are now allowed under the HOPE Act, with >100 transplants performed.
9.1 Pregnancy¶
Immunosuppression must be adjusted to prevent preterm labor and fetal growth restriction. Monitoring for hypertension and rejection is critical.
9.2 HIV-Positive Donors¶
HOPE Act allows HIV-positive donors; >100 transplants performed. Recipients require antiretroviral prophylaxis to prevent transmission.
10. KEY POINTS & CLINICAL PEARLS¶
- KDPI scores guide donor allocation. 2. Belatacept reduces CNI toxicity. 3. Non-HLA antigens and eplet mismatches contribute to rejection. 4. BK virus reactivation requires viral load monitoring and immunosuppression reduction. 5. Post-transplant lymphoproliferative disease is associated with Epstein-Barr virus.