This study found that kidney transplant recipients had higher hospital admission rates both overall and for many different disease groupings when compared to the general population. These results are consistent across the entire cohort and all the subgroup analyses. A similar observation of higher rates of hospitalization among kidney transplant recipients has been noted by Boubaker et al. who also reported that the most common causes of hospitalization in their study were infections and renal dysfunction . Abbott el al. noted that renal transplant recipients were at high risk for hospitalizations for cytomegalovirus disease and fractures [25, 26].
In this patient cohort, the two most common causes of hospitalization were infectious diseases and endocrine disorders. This finding is consistent with other studies [14, 24, 27, 28]. However, over the follow-up period of the study, the hospitalizations for these diseases have decreased greatly. For example, the incidence of infection has dropped from approximately 70% to between 15% and 44% . In our study, except for the first 60 days after a transplant procedure, close to 6% of total hospitalization was associated with infection through the study period. These reductions might be due to recent improvements in surgical techniques, immunosuppressive drugs, methods of diagnosis, and therapy. Urinary tract infection is the most common form of infection, and occurs in approximately 30% of patients within the first 3 months following transplantation . Cytomegalovirus (CMV) is also a common infection among renal transplant patients . The sole exception of an increased SHR was hospitalization due to complications of pregnancy which was likely due a much lower predisposition of transplant patients to become pregnant as these patients are likely older and may already have children or not want to become pregnant. Hospitalizations due to endocrine disorders are likely due to diabetes, a known complication of treatment with steroids. However the data are not granular enough to permit this to be ascertained.
The finding of the highest risk of hospital admission among those follow-up <60 days is not unexpected. This is likely related to the transplant procedure itself in addition to increased intensity of immune suppression during this period. Thereafter, SHR decreased over time, with a stable five-fold increased risk relative to the general population achieved at 3 years post transplant. The differences in hospitalization rates by province in particular between Ontario and BC or Atlantic region may be related to their follow-up care provision after transplant. In BC and Atlantic Canada patients are discharged to the community, and in the rest of the country (including Ontario) most care continues to be provided by the transplant centers.
Given the high quality and completeness in both CORR and DAD, it is reasonable to assume that losses to follow-up and primary diagnostic misclassification were low. As mentioned it has been estimated that <5% of hospital admissions would be missed across Canada (except Quebec), and therefore, the overall bias on the analysis should not be common. It is possible patients would be lost to follow-up if they moved outside the country after transplant procedure. However, given the medical needs of the kidney transplantation patients and the healthcare services provided within Canada, this number would be minimal.
Patients who underwent transplantation in 2004 could provide 2 years of hospital admission data for both pre transplant (2001 to 2003) and post transplant (2006 to 2008), allowing for a comparison of hospital admission between pre and post transplant except transplant procedure. The SHR decreased considerably pre to post transplant, from nearly 11 to approximately 5 suggesting that their overall health status improved significantly.
Caution should be exercised in interpreting the SHRs in this study. First, the DAD is an administrative database which only captures hospitalizations where patients were formally admitted to hospital and only those conditions severe enough to require hospitalization. It is unable to capture the morbidity among kidney transplant patients associated with increased visits to emergency departments where they are treated on an outpatient basis, or increased physician or prescription drug utilization. Second, biases may have been introduced from the patient selection process for transplantation. The selection criterion would differ by individual, and may reflect either a patient with optimum access to or with the most need for a transplant, or in sufficiently good health to be able to undergo transplantation. Since there is no patient level information on the criteria used to identify who underwent transplantation, the magnitude and the direction of the bias are unknown.