Introduction: Among end-stage kidney disease (ESKD) patients on dialysis with autosomal dominant polycystic kidney disease (ADPKD), relatively little is known about the epidemiology and risk factors for 30-day readmissions in the USA. Therefore, we evaluated the 30-day unplanned readmission rates and predictors and inpatient care costs among ESKD patients with and without ADPKD using a nationally representative, all-payer database. Methods: We utilized the Nationwide Readmissions Database from 2013 to 2018 to identify patients admitted for ESKD on dialysis with and without ADPKD using ICD-9 and ICD-10 codes. The primary outcome was a 30-day, unplanned readmission rate. Secondary outcomes were readmission reasons and timing, mortality, cost of hospitalization and rehospitalization, and adjusted predictors of readmissions. We used χ2 tests, t tests, and Wilcoxon rank-sum tests for descriptive analyses and survey logistic regression to calculate adjusted odds ratios and 95% confidence intervals for associations with readmissions adjusting for confounders. Results: From 2013 to 2018, in a cohort of 1,404,144 hospitalizations with ESKD on dialysis as the primary and secondary diagnosis on index admission, there were 8,213 (0.58%) patients with ADPKD and 1,395,932 patients without ADPKD. Those who had ADPKD during index admissions had fewer 30 days readmissions (18.8 vs. 23.8%, p < 0.0001). The cost of hospitalizations and readmissions in ESKD on-dialysis patients with ADPKD was higher than non-ADPKD patients. Compared to ESKD patients without ADPKD who were readmitted, readmitted ADPKD patients were more likely to be younger with a lower Elixhauser Comorbidity Index (ECI) score; have received kidney transplant, lower source of income, elective index admissions, private insurance; and be discharged routinely, admitted in hospitals with larger bed size, in teaching hospitals, and less likely to get admitted through the emergency department. Younger age (<75 years), higher ECI score, longer length of stay, Medicare and Medicaid insurance, self-pay, discharge to a short-term hospital, specialized care, home health care, and against medical advice were associated with significantly increased odds of readmission. ADPKD patients were 31% less likely to get readmitted and 43% less likely to die during readmissions. Discussion/Conclusion: Nationwide, ESKD on-dialysis patients with ADPKD were less likely to have 30-day readmission than patients without ADPKD. Inpatient mortality during readmissions in patients admitted with ESKD on dialysis was lower with ADPKD as compared to those without ADPKD at the cost of higher health care expenses.

© 2022 S. Karger AG, Basel

Introduction

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder predominantly resulting from a mutation in the polycystin-1 (PKD1) or polycystin-2 (PKD2) genes that causes fluid-filled cysts to develop and gradually grow in the kidneys [1, 2]. ADPKD is a systemic disease with numerous renal manifestations, including hypertension, proteinuria, and cyst hemorrhage as well as extrarenal manifestations, including polycystic liver disease, intracranial aneurysm, and pericardial effusion, which can be life-threatening [2]. Throughout a patient’s life, ADPKD frequently results in chronic kidney disease (CKD), characterized by a gradual loss of kidney function; and by age 60 years, approximately half of ADPKD patients develop end-stage kidney disease (ESKD). It is the most common genetic disorder to lead to ESKD [1-3].

Among patients with ESKD on dialysis with ADPKD, relatively little is known about the epidemiology and risk factors for 30-day readmissions in the USA, and in particular, there are no previous studies looking at 30-day unplanned readmissions as a measure of care quality in this patient population. Hospital readmissions are disruptive to patients and caregivers, put patients at additional risk of hospital-acquired infections and complications, and are costly to the health care system [4]. Additionally, reducing hospital readmissions has become a priority for health care throughout the USA to improve quality and decrease costs of care, and 30-day unplanned readmissions have been increasingly regarded as a key quality and reimbursement metric [4]. While other studies have looked at 30-day readmissions in patients with ESKD, patients with ESKD on dialysis due to ADPKD are generally younger and have less comorbidities compared to patients with ESKD on dialysis due to other causes; therefore, studies looking at ESKD patients, as a whole, do not represent this group [5]. In light of the potentially severe or lethal health outcomes and public health burden that can result from advanced progression of ADPKD, we believe it is a priority to better understand these hospitalization patterns to improve patient care and follow-up for these patients.

In this study, we seek to describe characteristics of hospitalizations in patients with ESKD on dialysis and ADPKD and compare it to patients with ESKD on dialysis due to other causes. We calculate readmission rates and hospitalization costs, investigate reasons for readmission, and evaluate readmission predictors in ADPKD patients in the USA using a nationally representative, all-payer database.

Materials and MethodsData Source

This retrospective cohort study uses the Nationwide Readmissions Database (NRD) from 2013 to 2018. The NRD is a database of all-payer hospital inpatient stays, developed for the Healthcare Cost and Utilization Project (HCUP), a Federal-State-Industry partnership, and is sponsored by the US Agency for Healthcare Research and Quality (AHRQ) [6]. This database is derived from HCUP’s State Inpatient Databases and is comprised of more than 100 clinical and nonclinical variables for each hospital stay, which enables research on national readmission rates, readmission rates in special populations, reasons for returning to the hospital for care, and the hospital costs for discharges with and without readmissions [6]. It contains verified patient linkage numbers, which can be used to track de-identified patients across hospitals within a state and single year [6].

The NRD provides nationally representative information on hospital readmissions for all types of payers and the uninsured. Unweighted, the NRD contains data from approximately 18 million discharges each year, and weighted, it estimates roughly 35 million discharges [6]. As of 2018, the NRD incorporates hospitalization discharge data from 28 geographically dispersed states, which encompasses 59.7% of the total US resident population and 58.7 of all US hospitalizations and continues to expand each year [6]. We used data from 2013 to 2018, which was the most recent data available to us at the time of this study.

Study Population and Design

We searched the NRD using the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code 585.6, and International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) code N18.6, to identify all admissions among patients ≥18 years old with a primary or secondary diagnosis of ESKD on dialysis. Patients with ADPKD were identified using the ICD-9-CM code 753.13 and ICD-10-CM code Q61.2. We excluded admissions related to pregnancy and chemotherapy to avoid routine readmissions, and we also excluded same-day readmissions which were considered a continuation of the index admission, deaths on index hospitalization, missing discharge disposition, length of stay (LOS) of less than 24 h, and admissions in December due to the lack of 30-day follow-up. Online supplementary Figure 1 (for all online suppl. material, see www.karger.com/doi/10.1159/000526923) outlines the creation of the study cohort.

We defined index admissions as hospitalization without any admission in the preceding 30 days, whereas readmissions were unplanned hospitalizations for any cause within 30 days of the index admission. As such, some individuals may have had several readmissions linked to an index admission as long as they were <30 days apart. We calculated readmission rates and reasons between the index admission and only the first readmission. We used ICD-9 and ICD-10 codes to determine the reasons for readmission. This study used de-identified, publicly available data, making it exempt from Institutional Review Board approval.

Definition of Covariates

We analyzed patient demographics, including age, gender, and median household income quartile based on the patients’ zip code. Age was further grouped into ≤55 years, 55–65 years, 65–75 years, and >75 years. The severity of overall illness and comorbid conditions were adjusted for using the Elixhauser Comorbidity Index (ECI) [7-9]. The weighted ECI score ranges from −7 to +12 and is based on 30 acute and chronic comorbidities associated with substantial increases in LOS, hospital charges, and mortality, and it is calculated for each patient by summing the individual weights of all comorbidities [7-9]. The ECI score was also grouped into ≤3, 4, and >4.

Index admission characteristics, including admission source, admission type, LOS, primary payer status, discharge disposition, and weekend admission, were also evaluated. LOS was further grouped into ≤2 days, 3–4 days, and >4 days. The primary payer was grouped into Medicare, Medicaid, private (including commercial and private plans), and other (self-pay, no charge, or other payer). Discharge disposition was categorized by routine or self-care, skilled nursing facility, short-term hospital, home health care, and against medical advice. We identified the admission type and source using the HCUP variables for emergency department and elective admission, respectively. We also evaluated several hospital characteristics, including hospital bed size, teaching status, urban-rural designation, and control (government vs. private). A detailed description of NRD data can be found at https://www.hcup-us.ahrq.gov/nrdoverview.jsp.

Outcomes Measured

Our primary outcome of interest was 30-day all-cause readmission and to determine the reasons for readmission. Online supplementary Table 1 in the appendix indicates the diagnosis categories and corresponding ICD-9-CM and ICD-10-CM codes. The secondary outcomes were readmission reasons and timing, cost of hospitalization and rehospitalization, and adjusted predictors of readmissions. Costs were inflation-adjusted using the US Bureau of Labor Statistics Consumer Price Index, with 2021 as the index base [10]. Lastly, we determined the association between ADPKD and 30-day readmission and mortality in patients with ESKD on dialysis.

Statistical Analysis

Descriptive statistics were used to compare the patient, admission, and hospital baseline characteristics between ESKD on dialysis with ADPKD and non-ADPKD with at least one 30-day readmission. We used Student’s T test for normally distributed continuous variables, χ2 for categorical variables, and Kruskal-Wallis for non-normally distributed continuous variables. Only weighted numbers were analyzed.

In the multivariable model, we evaluated the association between ADPKD and 30-day readmission using survey logistic regression to elucidate patient and hospital characteristics associated with unplanned readmissions while adjusting for age, ECI score, renal transplant, peritoneal dialysis, hemodialysis, admission type, LOS, primary payer, and discharge disposition. All significant levels were 2-sided, with a p value of <0.05 considered to be statistically significant. Analyses were done using SAS 9.4 (SAS Institute Inc.). We also evaluated the association between ADPKD and all-cause mortality during readmissions.

ResultsReadmission Rates, Reasons, Characteristics, and Mortality

From 2013 to 2018, in a cohort of 1,404,144 hospitalizations with ESKD on dialysis as the primary and secondary diagnosis on index admission, there were 8,213 (0.58%) patients with ADPKD and 1,395,932 patients without ADPKD. Of these ADPKD admissions, 1,560 (18.8%) were followed by at least one 30-day unplanned readmission and 354,574 (23.8%) readmissions among patients without ADPKD. Readmissions occurred throughout the 30-day period following the index hospitalizations with 32% and 55% of readmissions occurring within the first week and second week after discharge, respectively.

The most common reasons for readmission in ESKD on-dialysis patients with ADPKD hospitalizations were infection and inflammatory reaction due to the peritoneal dialysis catheter (4%); sepsis (3.9%); hypertensive CKD (3.8%); hyperkalemia (3.1%); pneumonia (2.7%); ADPKD (2.6%); complications due to the renal dialysis device, implant, and graft (2.2%); fluid overload (1.8%); acute respiratory failure (1.6%); and chest pain (1.5%) (Fig. 1a). The top ten reasons for unplanned 30-day readmission in ESKD on-dialysis patients without ADPKD were sepsis (6.4%); hypertensive CKD (5.2%); pneumonia (3%); hyperkalemia (2.9%); fluid overload (2.8%); complications due to renal dialysis device, implant, and graft (2%); infection and inflammatory reaction due to other cardiac and vascular devices (1.9%); non-ST elevation myocardial infarction (1.8%); acute respiratory failure (1.6%); and acute on chronic diastolic heart failure (1.5%) (Fig. 1b).

Fig. 1.

Top 10 primary causes of readmission in ESKD with (a) ADPKD and (b) non-ADPKD.

Table 1 presents the population characteristics of ESKD on dialysis admissions with and without ADPKD with at least one unplanned readmission. ADPKD patients were more likely to be younger (median [IQR] age 57 [47–66] versus 62 [51–72), p < 0.0001), have an ECI score ≤4 (85.7 vs. 75.9%, p < 0.000), indicating lower comorbidity burden, were more likely to have received a kidney transplant (11.3 vs. 4.6%, p < 0.0001), and have a lower source of income (17 vs. 13.9%, p < 0.0001). ADPKD patients with readmissions were less likely to get admitted through the emergency department (75.7 vs. 86.5%, p < 0.001), more likely to have elective index admissions (10.7 vs. 5.1%, p 0.0004), have private insurance (12.8 vs. 6.8%, p < 0.0001), and be discharged routinely (70.7 vs. 57.8%, p < 0.001). With respect to hospital characteristics, ADPKD readmitted patients were more likely to have been admitted in hospitals with larger bed size (67.1 vs. 60.5%, p 0.002), in teaching hospitals rather than to nonteaching hospitals (73.5 vs. 66.4%, p 0.0001) compared to readmitted patients without ADPKD. During readmissions, ESKD on-dialysis patients with ADPKD were less likely to die compared to those without ADPKD (3.9 vs. 6.1%, p < 0.001).

Table 1.

Baseline patient, admission, and hospital characteristics for ESKD on-dialysis patients without and with ADPKD with at least one unplanned readmission

Significant Predictors of Unplanned Readmission

Multivariate analysis revealed that ADPKD was associated with decreased odds of readmission (adjusted odds ratio [aOR]: 0.79, 95% confidence interval [CI]: 0.72–0.87, p < 0.001). Younger age: age ≤55 years (aOR 1.22, 95% CI: 1.2–1.24, p < 0.001), age 55–65 years (aOR 1.12, 95% CI: 1.09–1.14, p < 0.001), and age 65–75 years (aOR 1.06, 95% CI: 1.04–1.08, p < 0.001), females (aOR 1.07, 95% CI: 1.05–1.08, p < 0.001), higher ECI score = 5 (aOR 1.07, 95% CI: 1.05–1.09, p < 0.001), and ECI score ≥ 6 (aOR 1.15, 95% CI: 1.11–1.19, p < 0.001) were associated with increased odds of readmission. Index admission characteristics associated with increased odds of readmission included those admitted to the emergency department (aOR 1.15, 95% CI: 1.11–1.19, p < 0.001), have nonelective admissions (aOR 1.28, 95% CI: 1.23–1.33, p < 0.001), have longer LOS: LOS 3–4 days (aOR 1.03, 95% CI: 1.02–1.05, p < 0.001), LOS 3–4 days (aOR 1.16, 95% CI: 1.14–1.18, p < 0.001), have Medicare (aOR 1.30, 95% CI: 1.27–1.33, p < 0.001), Medicaid (aOR 1.45, 95% CI: 1.41–1.50, p < 0.001), with self-pay (aOR 1.17, 95% CI: 1.10–1.24, p < 0.001), discharged to a short-term hospital (aOR 1.27, 95% CI: 1.18–1.37, p < 0.001), discharged to specialized care (aOR 1.24, 95% CI: 1.22–1.26, p < 0.001), have home health care (aOR 1.26, 95% CI: 1.24–1.28, p < 0.001), against medical advice (aOR 1.66, 95% CI: 1.60–1.73, p < 0.001), and admitted to metropolitan hospitals (aOR 1.22, 95% CI: 1.18–1.27, p < 0.001) (Fig. 2). The odds ratio of 30-day mortality during readmissions was significantly lower in ESKD on-dialysis patients with ADPKD compared to those without ADPKD (OR 0.57, 95% CI: 0.41–0.81, p < 0.002).

Fig. 2.

Predictors of unplanned readmissions for ESKD patients on dialysis.

Costs

Figure 3 summarizes the mean cost of index hospitalization and readmission for ESKD with and without ADPKD. The mean cost of index hospitalizations in those without ADPKD was $12,394, as compared to those with ADPKD which was $15,093 (p < 0.0001). The mean cost of readmissions in those without ADPKD was also lower compared to those with ADPKD ($16,455 vs. $17,391; p < 0.0001).

Fig. 3.

Mean total cost of index hospitalizations and readmissions in ESKD on-dialysis patients with and without ADPKD.

Conclusion

Using a nationally representative sample, we described characteristics of hospitalizations in patients with ESKD on dialysis with and without ADPKD. We found that ESKD on-dialysis patients with ADPKD had a lower proportion of 30-day hospital readmissions than patients without ADPKD. Other than readmissions for kidney transplant being higher in patients with ESKD on dialysis and ADPKD, other reasons for readmission in the two groups were similar. Having ESKD and ADPKD was associated with significantly lower odds of hospital readmission and readmission mortality compared to having ESKD without ADPKD.

Patients with ESKD on dialysis and ADPKD were less likely to have hospital readmissions than patients with ESKD on dialysis non-ADPKD. This may partly be explained by the differences seen in patient demographics. Patients with ESKD on dialysis and ADPKD were younger, had less comorbidities, and were less likely to die than patients with ESKD non-ADPKD. This finding is consistent with prior studies that compared ESKD ADKPD patients with non-ADPKD patients [5]. Patients with ESKD on dialysis with ADPKD were more likely to have a routine discharge, again suggesting that patients during index hospitalization were healthier than ESKD on dialysis non-ADPKD patients. There were also differences in hospital characteristics, with ESKD ADPKD patients being admitted for elective admissions to hospitals that were larger teaching hospitals. The differences in hospital characteristics may be related to the higher proportion of patients with ESKD on dialysis and ADKPD with kidney transplant.

Despite lower rates of readmissions, nearly 1 out of 5 hospitalizations will result in hospital readmission. In an earlier study focused on patient-important outcomes for ADPKD found that for patients and caregivers, kidney function, delayed progression to ESKD, and survival were the top priorities, with an emphasis on achieving normality and maintaining control over health and lifestyle [11]. In the context of our findings, this further underscores the importance of reducing avoidable readmissions among ADPKD patients, which can contribute to significant lifestyle disruption and reduced quality of life.

Infection-related readmissions were common in both ADPKD and non-ADPKD groups. This is consistent with our prior research that infection-related readmissions are common in patients on dialysis [12]. Cardiac-related reasons for patients with ESKD on dialysis and ADPKD were half as common as in the ESKD on the dialysis non-ADPKD group. This is likely related to the primary causes of ESKD in non-ADPKD patients, with diabetes and hypertension being top causes of ESKD in the USA. [10].

The cost of hospitalizations and readmissions in ESKD on-dialysis patients with ADPKD were higher than in non-ADPKD patients. There was no difference in hospital LOS. Given the higher comorbidity burden and high proportion of patients with nonroutine discharges, we had expected that the cost of index hospitalization would be higher in patients with ESKD on dialysis without ADPKD. Unfortunately, we are unable to provide additional details into what factors contributed to the higher cost of index hospitalization and readmission in patients with ESKD on dialysis and ADPKD.

Reducing index admission costs may improve overall cost-effectiveness, but a substantial driver of episode costs comes from readmissions that account for 54% of the total, which could be alleviated by efforts to reduce unplanned readmissions. Previous HCUP studies focused on inpatient care for ADPKD focused primarily on kidney transplantation outcomes and complications, but there is no previous research specifically focused on readmissions among ADPKD patients to compare our findings to [11, 13-15]. To build on the findings from this study, we believe additional research focused on specific predictors of readmission in ADPKD patients could be beneficial to understanding and identifying high-risk patient subgroups.

This study has several strengths. The first is that it uses nationally representative, longitudinal data across all payers and can be considered generalizable to the US population. The NRD also provides extensive data for over 100 clinical and nonclinical variables that enabled us to interrogate various patient, admission, and hospital characteristics in addition to cost and readmission reasons. Our analysis included a large sample of hospital readmissions over several years (n = 3,395,433), which provided us with adequate statistical power to identify predictors of 30-day readmissions.

However, this study also has several limitations which should be considered in the context of these findings. Since the NRD only includes data on inpatient care, we could not assess some important clinical and lifestyle factors and their effects on readmission rates, such as outpatient dialysis, medication use or adherence, smoking, and diet. We also lacked lab data, post-discharge follow-up information, and any encounters with outpatient care. We also were not able to evaluate any potential confounding effects based on race or ethnicity since these variables were not included in the data.

In summary, this study addresses an important unmet need in ESKD patients with ADPKD research by providing national estimates of 30-day hospital readmissions and identifying several important factors such as the reasons for readmission and associated inpatient care costs. On a national level, ESKD on-dialysis patients with ADPKD were less likely to have 30-day readmission than patients without ADPKD. The incidence of mortality during readmission was lower in ESKD on-dialysis patients with ADPKD compared to those without ADPKD. Costs associated with ESKD on-dialysis patients with ADPKD are high in index admission and on readmission compared to non-ADPKD patients.

Statement of Ethics

This study used de-identified, publicly available data, making it exempt from Institutional Review Board approval.

Conflict of Interest Statement

Dr. Nadkarni reported being a scientific co-founder, consultant, advisory board member, and equity owner of Renalytix AI; a scientific co-founder and equity holder for Pensieve Health; a consultant for Variant Bio; and receiving grants from Goldfinch Bio and personal fees from Renalytix AI, BioVie, Reata, AstraZeneca, and GLG consulting. Dr. Nadkarni is supported by NIH Grants R01-DK108803 and R01-HL155915. Dr. Chan is supported in part by a grant from the NIH/NIDDK (K23DK124645). Dr. Chan is a consultant for Vifor Pharma INC. and has received honorarium from Fresenius Medical Care.

Funding Sources

The authors received no funding for this study.

Author Contributions

Aparna Saha conceptualized and designed the study. She performed the statistical analysis and assisted in drafting and critically revising the manuscript. She approves the final version of the manuscript. Paulette Erickson conceptualized and designed the study project. She assisted in the statistical analysis and drafted and critically revised the manuscript. She approves the final version of the manuscript. Cristina Liriano Cepin assisted in the interpretation of the results, in drafting, and critical revision of the manuscript. She approves the final version of the manuscript. Girish N. Nadkarni assisted with data acquisition, interpretation of the data for the work, assisted in drafting the manuscript, and approves of the final version. Lili Chan interpreted the data and drafted and critically revised the manuscript. She approves the final version of the manuscript.

Data Availability Statement

This study used de-identified, publicly available data. Details on how to obtain the NRD can be found on the HCUP-AHRQ website (https://www.hcup-us.ahrq.gov/nrdoverview.jsp).

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