Tissue plasminogen activator, its fast acting plasma inhibitor and protein C after renal transplantation

Hypercoagulability in renal transplant recipients. Identifying patients at risk of renal allograft thrombosis and evaluating strategies for prevention

Renal transplantation improves survival and quality of life for patients with end-stage renal disease (ESRD). Improvements in immunosuppressive therapy have reduced early allograft loss due to acute rejection to very low levels. Early allograft loss, due to acute thrombotic complications, remains a constant and proportionally increasing complication of renal transplantation. Identifying risk factor(s) for thrombosis amenable to preventive strategies has been elusive. Epidemiological studies have attempted to define risk in terms of modifiable (drugs, dialysis modality, surgical procedure) and non-modifiable (age, diabetes mellitus, vascular anomalies) factors, or identify changes in coagulation or fibrinolysis promoting a more thrombotic state. Most recently the evolution of thrombophilia research has established the potential for inherited hypercoagulability to predispose to acute allograft thrombosis. Inheritance of the factor V Leiden (FVL), prothrombin G20210A mutation, or the presence of antiphospholipid antibodies (APA) may increase the risk of renal allograft thrombosis approximately 3-fold in selected patients. Patients with ESRD due to systemic lupus erythematosus (SLE) appear at particularly high risk of thrombosis, especially if they have either APA or detectable beta(2)-glycoprotein-1. Data for other hypercoagulable states such as hyperhomocystinemia or the C677T polymorphism of the methylenetetrahydrofolate reductase gene are deficient. Patients with APA, FVL, or prothrombin G20210A mutation also appear to have greater graft loss due to vascular rejection, possibly reflecting immunological injury upon the vascular wall exacerbated or induced by the prothrombotic state. While substantial in vitro data suggest cyclosporine is prothrombotic, an independent clinical association with allograft thrombosis is unproven. Interventions to reduce thrombotic risk including heparin, warfarin, and aspirin have been evaluated in both selected high-risk groups (heparin and warfarin) and unselected populations (heparin and aspirin). In unselected patients at low clinical risk, aspirin (75-150 mg/day) with or without a short period of unfractionated heparin (5000U twice a day for 5 days) appears to reduce the risk of renal allograft thrombosis significantly with a low risk of bleeding, especially when compared with low molecular weight heparins which risk accumulation in renal failure. In high-risk groups (identified thrombophilic risk factor, previous thrombosis, or SLE) longer period of heparin, with or without aspirin and maintenance with warfarin, should be considered. Re-transplantation following graft loss due to vascular thrombosis can be undertaken with a low risk of recurrence. Further prospective studies evaluating both putative risk factors and intervention strategies are required to determine whether routine clinical screening for thrombophilic factors is justified.

Renal allograft thrombosis: can thrombophilia explain the inexplicable?

Renal allograft thrombosis remains a preventable cause of early allograft thrombosis. It should not be considered simply an unpredictable and poorly understood consequence of surgery. Extrapolated data from the general population and early data from renal patients supports the concept that the interplay of non-inherited hypercoagulability of renal disease with inherited thrombophilia, and the altered environmental milieu of transplantation predisposes to thrombosis (summarized in Figure 2). We should not accept the inevitability of a constant attrition of grafts to thrombosis and need to continue to identify risk factors and confirm appropriate screening and interventions for its prevention, almost certainly requiring collaborative multicentre trials. In the future, just as we now expand the specificity of HLA gene typing with molecular biology, genotyping for recognized thrombophilia genes in patients at risk will expand our ability to recognize and prevent thrombosis with targeted interventions drawn from the increasing array of anticoagulants now available. The contribution of thrombophilia to non-immune mechanisms of chronic allograft loss is also a potentially important but neglected area of research.

Early loss of renal transplants in patients with thrombophilia

BACKGROUND

We considered the possibility that thrombophilia may propagate graft thrombosis and therefore we evaluated the protein C system, which is a natural anticoagulant. Potential alterations in this system include protein C or protein S deficiency, inhibition through a lupus anticoagulant (LA), or a resistance to activated protein C due to the factor V Leiden (FVL) mutation.

METHODS

One hundred thirty-two consecutive renal transplant patients, not known to have abnormal thrombostasis, in whom 1-year graft survival could be assessed, underwent laboratory testing for protein C or S activity, LA, and FVL. Transplant survival and demographic data were extracted from the hospital record.

RESULTS

We identified 18 patients with thrombophilia (FVL, 10; LA, 6; protein S, 2) who had received a total of 28 renal transplants. Of these 28 transplant recipients, 11 transplants were lost within the first year, compared with 21 of 155 transplants to 114 patients without thrombophilia (P=0.0003). Median graft survival for patients with thrombophilia was 30 months (range: 0 to 166), compared with 86 months (range: 0 to 212) for patients without thrombophilia (P<0.01). The presence of thrombophilia represented a 3.5-fold (95% confidence interval, 2.3-5.3-fold) risk for 1-year graft loss.

CONCLUSION

In this retrospective study, patients with thrombophilia had a significantly higher risk of early transplant failure. These data point toward a potential contribution of thrombophilia to transplant loss, a hypothesis that needs further study.