Abstract
Objective:
Polycystic kidney disease (PKD) is a clinically and genetically heterogeneous class of genetic disorders characterized by development of renal cysts leading to renal failure and end stage renal disease (ESRD). Autosomal dominant polycystic kidney disease (ADPKD) accounts for the majority of PKD cases and is the predominant monogenic cause of ESRD. Limited information on patient characteristics and healthcare resource utilization is available in this population. This study assessed hospital-based inpatient utilization of patients with ADPKD in the US to help further understand the disease, which may lead to treatments that delay progression and reduce healthcare resource utilization.
Methods:
A cross-sectional analysis was conducted using MedAssets Health System Data to investigate inpatient resource utilization for a total of 1876 patients hospitalized with ADPKD or chronic kidney disease (CKD). Patient characteristics and inpatient resource utilization were compared between hospitalized patients with ADPKD and CKD, including demographic and clinical characteristics, overall health, rates of complications and surgical interventions, and average length of hospital and intensive care unit stay.
Results:
Compared with patients with CKD, patients with ADPKD were more likely to have commercial insurance as their primary payer (36.1 vs 17.8%) and were significantly younger (mean age 57.9 vs 69.5 years) and generally healthier (Charlson Comorbidity Score of 2.0 vs 3.3). Patients with ADPKD also had a substantially shorter average length of hospital stay (6.3 vs 10.3 days). However, patients with ADPKD experienced more kidney-related complications and a higher surgical procedure rate (mainly for transplant and complete nephrectomy).
Conclusions:
Although patients with ADPKD were generally healthier than patients with CKD, specific kidney function complications were more frequent. Patients with ADPKD had a higher rate of major kidney procedures, which may contribute to the high burden of ADPKD-related hospital-based inpatient resource utilization.
Introduction
Polycystic kidney disease (PKD), a clinically and genetically heterogeneous class of genetic disorders characterized by renal cysts, is a leading cause of end stage renal disease (ESRD)Citation1–3. In addition, ‘environmental’ renal cysts may develop in individuals after many years of dialysisCitation4–6. Autosomal dominant polycystic kidney disease (ADPKD) accounts for the majority of all PKD casesCitation7, and is the primary inheritable cause of ESRDCitation8,Citation9.
Disease progression of ADPKD is marked by declining kidney function, along with increasing frequency and intensity of acute hospitalizations. Hallmarks of ADPKD include the development of numerous fluid-filled renal cysts resulting in enlargement of the kidneys, renal insufficiency and failure, and, ultimately, in ESRDCitation10,Citation11. In addition, in ADPKD patients, hypertension is an early identifiable marker of renal and cardiovascular diseaseCitation7,Citation11. Additional renal complications with ADPKD include urinary tract infections and renal stonesCitation7,Citation12. Furthermore, ADPKD is a systemic disease with extra-renal complications arising from cysts developing in organs beyond the kidneys, including the liver and pancreas. Additional extra-renal complications include intracranial aneurysms, other vascular events, cardiac events, and hematuriaCitation7,Citation12–14.
To date, only a few studies on the humanistic and economic burden of ADPKD have been conductedCitation15–19, and little is known regarding patient characteristics and hospital-based healthcare resource utilization for patients with ADPKD. A previous analysis of ADPKD disease progression in a natural history study between 1978 and 2012 showed that a difference in the estimated glomerular filtration rate decline can be predicted at least 10 years prior to the onset of ESRD, indicating that high-risk patients can be identified early for treatmentCitation20. A better understanding of ADPKD, including patient characteristics, disease progression, and hospital-based healthcare resource utilization, is necessary to help improve treatments of disease complications that may delay progression, increase patient quality-of-life, and reduce the healthcare resource utilization associated with this disease.
This study was designed to assess hospital-based inpatient utilization in patients with ADPKD. The objective of the study was to investigate and compare patient characteristics and hospital-based healthcare resource utilization between patients with ADPKD and patients with chronic kidney disease (CKD), as substantial information is available regarding patient characteristics and healthcare resource utilization for CKDCitation21–23. The current analysis evaluated demographic and clinical characteristics, baseline health and comorbidities, rates of complications and surgical interventions, and average length of stay in the hospital and intensive care unit (ICU).
Patients and methods
Patient population and study design
A cross-sectional analysis was conducted of inpatient resource utilization in patients hospitalized with ADPKD compared with patients hospitalized with CKD using data from MedAssets Health System Data of de-identified patient level claims and billing records for 390 hospitals within the US. Data are extracted daily from hospital billing systems ∼30 days post-discharge and records are pooled, cleansed, de-identified, and uploaded to the analytic warehouse on a weekly schedule.
The analysis for this study was performed on individual hospital discharges ranging between January 1, 2010 and December 31, 2012 (therefore, patients could have been included more than once if they had more than one unique discharge). Patients included in the ADPKD cohort were ≥18 years of age and had a diagnosis of ICD-9-CM for Unspecified PKD (753.12) or ADPKD (753.13); patients with a primary or secondary diagnosis of autosomal recessive polycystic kidney disease (ARPKD; 753.14) were excluded. Patients included in the CKD cohort were >18 years of age and had a diagnosis of ICD-9-CM for CKD (585.1–585.9); patients with a primary or secondary diagnosis of Unspecified PKD, ADPKD, or ARPKD (753.12, 753.13, or 753.14) were excluded, as were patients with primary or secondary cystic kidney disease (753.1). Only patients with ADPKD or CKD as a primary diagnosis were included in this analysis (patients who had ADPKD or CKD and were hospitalized for another primary condition were not included).
Outcomes
Patient demographics, including age, gender, primary payer, and CKD staging (CKD stage 1, ICD-9-CM code 585.1; CKD stage 2, 585.2; CKD stage 3, 585.3; CKD stage 4, 585.4; CKD stage 5, 585.5; ESRD, 585.6; CKD unclassified, 585.9), as well as hospital characteristics, including geography, urban/rural, bed size, teaching status, and ownership, were compared between the ADPKD and CKD cohorts. The comparisons included descriptive statistics and bivariate statistics (T-tests for continuous variables and Chi-square tests for categorical values).
Overall health characteristics were compared for the ADPKD and CKD cohorts based on the Charlson Comorbidity Index, as well as individual comorbiditiesCitation24,Citation25. The comparisons included descriptive statistics and bivariate statistics (T-tests for continuous variables and Chi-square tests for categorical values). A multivariate regression was performed to estimate the total number of comorbidities using a negative binomial model.
Disease-related complications, nephrology procedures, and resource utilization were compared between the ADPKD and CKD cohorts by examining inpatient complication rates (percent) for individual complications and surgical procedure rates per 1000 discharges. Complications (ICD-9-CM diagnosis code) included in the analysis were: ESRD (585.6), kidney failure (acute, 584.1–584.5; non-acute, 586), renal/hemodialysis (39.95), hypertension (401–405), hyponatremia (276.1), aneurysm (437.3), mitral valve prolapse (424.0), urinary tract infection (599.0), kidney infection (590.0–590.9), and kidney stones (592.0). Analyzed procedures (ICD-9-CM procedure code) included nephrotomy and nephrostomy (55.0), pyelotomy and pyelostomy (55.1), diagnostic procedures on kidney (55.2), local excision or destruction of lesion or tissue of kidney (55.3), partial nephrectomy (55.4), complete nephrectomy (55.5), transplant of kidney (55.6), other repair of kidney (55.8), and other kidney operations (55.9).
Length of hospital stay was defined as the number of days from admission to discharge; length of ICU stay was calculated based on daily ICU charges from detailed hospital billing records. Unadjusted comparisons included descriptive statistics and bivariate statistics (T-tests for continuous variables and Chi-square tests for categorical values). Multivariable regression models were created to estimate the count of comorbidities, length of stay, and ICU length of stay. The primary outcome variables were accessed using a negative binomial distribution to adjust for the imbalance commonly found in count/interval data distributions.
Results
Study population
The base study sample consisted of 11,023 patients hospitalized and discharged—10,164 with a primary diagnosis of CKD and 859 with a primary diagnosis of ADPKD. For statistical purposes, a random 10% sample was selected from the overall CKD population for comparison to the ADPKD cohort. The purpose of this was to ensure that the CKD influence was not over-estimated, which would not permit enough precision for ADPKD in the modelCitation26,Citation27. Comparative analysis between the overall CKD population and 10% sample showed no significant differences across all patient demographic and diagnostic characteristics (data not shown). The analyses presented here include a total of 1876 patients; 859 with a primary diagnosis of ADPKD and 1017 with a primary diagnosis of CKD ().
Figure 1. Study schematic.
Patients with ADPKD were significantly younger than CKD patients (); 75.6 vs 46.9% of patients were ≤60 years old and patients with ADPKD had a mean age of 57.9 years compared with 69.5 for CKD patients (±15.9 and ±15.5, p < 0.0001) (not shown in ). ADPKD patients were more likely to have commercial insurance as their primary payer (36.1 vs 17.8%, p < 0.0001) and a lower percentage of patients in the ADPKD cohort were in ESRD (49.8 vs 84.8%, p < 0.0001). However, 27.2% of patients with ADPKD had an unknown or unclassified CKD stage compared with 0% of CKD patients. Compared with the CKD cohort, patients with ADPKD were primarily admitted to larger hospitals with >500 beds (43.0 vs 26.3%, p < 0.0001) and were more likely to be at major teaching facilities (50.2 vs 36.1%, p < 0.0001) and/or government-owned facilities (20.3 vs 8.1%, p < 0.0001) ().
Table 1. Patient demographic characteristics.
Table 2. Comparison of ADPKD and CKD discharge hospital characteristics.
Overall health
Patients with ADPKD were generally healthier (with fewer comorbidities) compared with the CKD cohort and had a significantly lower mean Charlson Comorbidity Index score of 2.0 vs 3.3, respectively (). Specific individual comorbidities with a significantly lower frequency in patients with ADPKD compared with the CKD cohort (p < 0.0001) included congestive heart failure (4.7 vs 19.3%), peripheral vascular disease (1.3 vs 5.8%), cerebrovascular disease (1.5 vs 4.8%), diabetes (9.4 vs 29.3%), and moderate or severe renal disease (73.8 vs 100.0%). Other comorbidities statistically lower in patients with ADPKD (p < 0.05) included chronic pulmonary disease, rheumatic disease, moderate or severe liver disease, malignancy, and HIV/AIDS. After controlling for age and other clinical factors, the ADPKD cohort was associated with 80% (p < 0.0001) fewer comorbidities compared with the CKD cohort (IRR = 0.19, confidence interval [CI] = 0.15–0.24) ().
Table 3. Comparison of ADPKD and CKD Charlson comorbidities.
Table 4. Negative binomial regression model estimating total number of comorbidities, total length of stay, and total ICU length of stay.
Disease-related complications and inpatient resource utilization
Patients with ADPKD had significantly lower rates of ESRD (49.7 vs 84.9%, p < 0.0001) and hyponatremia (27.5 vs 41.0%, p < 0.0001), but higher rates of hypertension (83.8 vs 60.2%, p < 0.0001), acute kidney failure (10.9 vs 5.3%, p = 0.008), kidney infection (7.7 vs 5.0%, p = 0.0142), and kidney stones (3.5 vs 0.5%, p < 0.0001) compared with patients with CKD ().
Table 5. Comparison of ADPKD and CKD inpatient disease-related complication rates and surgical procedure rates.
Patients with ADPKD also had a higher surgical procedure rate of 868.5 procedures per 1000 discharges compared with 154.4 procedures per 1000 discharges for the CKD cohort (p < 0.0001) (). The principal surgical procedures contributing to the difference were transplant (506.4 per 1000 discharges for the ADPKD cohort vs 142.6 for the CKD cohort) and complete nephrectomy (323.6 per 1000 discharges for the ADPKD cohort vs 10.8 for the CKD cohort). Along with surgical procedures, patients with ADPKD also had a slightly higher rate of ICU discharges (27.7 vs 21.0%).
Overall hospital length of stay and ICU length of stay were compared for patients with ADPKD and the CKD cohort. Mean unadjusted overall length of stay was lower for patients with ADPKD compared with the CKD cohort (6.3 ± 4.6 vs 10.3 ± 10.3, p < 0.0001). No significant differences were observed in mean unadjusted ICU length of stay in patients with ADPKD compared with the CKD cohort (2.8 ± 3.7 vs 2.5 ± 2.8, p = 0.3652). After controlling for patient demographics, hospital location, co-morbid conditions, and surgical procedures, the ADPKD cohort was predicted to have a 44% shorter average length of stay compared with the CKD cohort (p < 0.0001), with no difference in ICU length of stay (p = 0.3652). The regression analysis is shown in .
Discussion
This study shows that patients with ADPKD were significantly younger than CKD patients, were more likely to have commercial insurance as their primary payer, and were more likely to be treated at large (500+ bed) major teaching hospitals. Patients with ADPKD had fewer comorbidities compared with CKD patients; however, they experienced more kidney-related complications, such as hypertension, acute kidney failure, kidney infection, and kidney stones, and had a higher surgical procedure rate compared with patients with CKD. Additionally, patients with ADPKD had a significantly shorter average length of hospital stay than similar CKD patients. The information regarding patients with ADPKD identified in this study could contribute to possible intervention for the disease, which could in turn delay the onset of symptoms. Because patients can be identified earlier, opportunities for treatment intervention can be identified based on the severity of the disease.
A better understanding of ADPKD patient characteristics and hospital-based healthcare resource utilization may lead to improved treatment of disease complications. Two recent studies investigated ADPKD patient characteristics and treatment patterns over time. One study observed patients initiating renal replacement therapy and compared patients with ADPKD with non-ADPKD controlsCitation28; the second study compared patients with ADPKD who were diagnosed between 1961–1990 with a cohort diagnosed between 1991–2011Citation29. Both studies provided general information regarding patients with ADPKD, but did not include specific hospital-related characteristicsCitation28,Citation29. Martinez et al.Citation28 found that ADPKD patients were younger at initiation of renal replacement therapy and had a lower frequency of most comorbidities, with the exception of hypertension (a disease-related complication), compared with non-ADPKD patients. Additionally, recent studies demonstrate that ADPKD has a negative impact on patient quality-of-life, primarily due to abdominal pain and discomfortCitation15–18.
Compared with other studies examining ADPKD patient characteristics, the current study specifically investigated demographics and inpatient resource utilization in patients with ADPKD compared with those with CKD in the hospital setting. Information regarding disease-related complications and inpatient resource utilization may help to identify treatments to delay or prevent the progression of ADPKD, as these outcomes are measurable prior to extensive renal function decline, and thus may be useful indicators for early intervention. The clinical and demographic characteristics of patients hospitalized with ADPKD compared with CKD identified in this study adds to the currently limited body of knowledge on patient-specific characteristics for ADPKD. The data show that geographic areas are similar between ADPKD patients and CKD patients, which is not surprising. The differences observed in hospital size based on bed number, hospital ownership, and private insurance could be predicted based on the fact that ADPKD is more frequently treated at larger hospitals with Centers for Excellence, and that ADPKD patients are generally younger than patients with CKD. Typically, a higher percentage of older patients and patients in ESRD are on Medicare compared with commercial insurance.
As shown in previous studies, this research also found that hospitalized patients with ADPKD were younger, with fewer comorbidities compared with patients with CKD. Additionally, patients with ADPKD were predicted to have 80% fewer comorbidities when controlling for age and other clinical factors. Compared with CKD patients, patients with ADPKD had lower rates of the comorbidities investigated here, with the exception of old myocardial infarction, which was not significantly different between the cohorts. Summarized in a review by EcderCitation30, various studies have shown that cardiovascular complications are a major cause of morbidity and mortality in patients with ADPKD and also that hypertension is a common finding for patients with ADPKD. While hypertension was significantly more frequent in the ADPKD population, congestive heart failure, peripheral vascular, and cerebrovascular disease were all significantly lower.
Patients with ADPKD had lower rates of ESRD and hyponatremia, but higher rates of acute hypertension, kidney failure, kidney infection, and kidney stones. The frequency of total surgical procedures was higher for patients with ADPKD compared with CKD, primarily due to an increased rate of major kidney procedures, which include complete nephrectomy and kidney transplant. The increased rate of kidney transplant may be related to the increased general health of patients with ADPKD compared with those with CKD. Overall, patient outcomes are better when comparing transplant with dialysis, as transplant procedures generally increase survival and improve quality-of-life. A study of survival trends from 1977–2007 shows that decreased annual mortality trends were seen in patients with transplantation vs dialysisCitation31. Additionally, pre-emptive transplant provides substantial patient benefitCitation32, and kidney transplant in elderly patients weakens the age-associated increase in mortality that is generally seenCitation33. Dialysis before transplantation does appear to play a role in outcomes—early graft function rates have been shown to be better for peritoneal dialysis compared with hemodialysisCitation34.
Although there was a higher rate of surgical procedures in the ADPKD cohort, unadjusted average length of hospital stay was shorter in this cohort compared with the CKD cohort. After regression adjustment, patients with ADPKD were predicted to have a 44% shorter hospital stay. There was no difference in the adjusted length of ICU stay between the two cohorts.
While the data presented here do effectively highlight ADPKD patient characteristics and hospital-based healthcare resource utilization, there are some limitations to the study. The study included only hospital-based resource utilization, so data on observation stays and day procedures are not included. Additionally, the analysis presented here focused only on patients with ADPKD or CKD as a primary diagnosis; therefore, patients with ADPKD hospitalized with a different primary diagnosis (e.g., ESRD) were not accounted for. Because there is no treatment for ADPKD, coding for ADPKD may be under-utilized, resulting in the exclusion of additional patients with ADPKD. To maximize the ADPKD dataset, patients categorized as ‘PKD unspecified’ were included in the ADPKD cohort and may have erroneously included patients with ARPKD; however, because patients <18 were excluded, any inclusion of ARPKD patients was minimized. The data presented here represent hospital billing-based accounting data. The data are coded for reimbursement purposes, not for patient disease management, and therefore do not employ a protocol-driven data collection method. However, these data do represent a real-world view of the ADPKD patient population within the hospital setting.
Conclusions
This study confirmed the expectation that patients hospitalized with ADPKD are significantly younger than CKD patients and more likely to have commercial insurance as their primary payer. Although patients with ADPKD are generally healthier, specific complications relative to kidney function are more frequent. Additionally, patients with ADPKD have a higher rate of major kidney procedures compared with CKD patients, contributing to the high burden of ADPKD-related hospital-based resource utilization. Further studies will focus on additional aspects of ADPKD patients, including health economics analyses.
Transparency
Declaration of funding
This study was sponsored by Otsuka America Pharmaceutical, Inc., Princeton, NJ. Medical writing and editorial support for the preparation of this manuscript was provided by Scientific Connexions, Inc., Lyndhurst, NJ, funded by Otsuka America Pharmaceutical, Inc.
Declaration of financial/other relationships
CB & BG were employees of Otsuka America Pharmaceutical, Inc. at the time this study was conducted. SR is a current employee of Otsuka America Pharmaceutical, Inc. CC & KB are employees of MedAssets, Inc., which has received funds from Otsuka America Pharmaceutical, Inc. in connection with the conduct of this study. DL is an employee of Outcomes Insights, Inc., which has received funds from Otsuka America Pharmaceutical, Inc. in connection with the conduct of this study. JME peer reviewers on this manuscript have no relevant financial or other relationships to disclose.
Acknowledgments
The authors would like to acknowledge Scientific Connexions, Inc., for assistance in the preparation of this manuscript for submission.
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