The Role of Caregiving in Healthcare Utilization Among Obese Living Kidney Donors
Conditions: Utilization, Health Care, Obesity
Sponsor: University of Alabama at Birmingham

Title: Healthcare Utilization in Obese Caregiver Living Donors 
NCT04341896  
Date: December 16, 2024 
Study Protocol and Statistical Analysis Plan (with Results) 
 
 

PROTOCOL 
 
Study population. 25,352 donors from 278 centers will be studied. Contact information for donors was 
provided by the Scientific Registry of Transplant Recipients (SRTR) and is verified using Lexis Nexis Accurint. 
We anticipate that approximately 20% (n=5,070) of this cohort 
will have served as the primary caregiver for their recipient. 
Characteristics of the overall cohort and the subset of 
caregiver donors are in Table 1. Moreover, the subset of 
caregivers > 50 years is greater than the whole cohort, further 
highlighting the need for aging research in this population. 
 
Donor questionnaire. All participants are contacted through 
a centralized phone bank maintained by the parent R01’s PI at UAB and are administered a survey by phone, 
mail, or email. The following data are collected and maintained using a robust, redundant, secure, web-based 
computer entry system (REDCap): demographics (gender, date of birth, race/ethnicity); socioeconomic 
(education, employment, marital status); family history of comorbid disease; follow-up (frequency of doctor 
visits pre and post-donation); comorbidities pre and post-donation (smoking, cardiovascular disease, diabetes, 
etc.), current hypertension, diabetes, or chronic kidney disease/end-stage renal disease, and mental health 
quality of life. Patients are contacted for follow-up surveys annually. Furthermore, we will leverage the 
infrastructure of the parent R01 to collect new primary data specific to caregivers. Among those who were the 
primary caregivers for their recipients, we will administer additional questions derived from the Bakas 
Caregiver Outcomes Scale and National Alliance for Caregiving quantitative interviews, to describe their 
physical and mental health at time of donation, including self-reported caregiver burden and benefit pre and 
post-donation, the economic impact of caregiving, and the caregiving role in the context of donation.  
 
Medical records abstraction. During completion of the questionnaire, donors are asked to provide signed 
waivers for medical records requests from their primary and other care providers. Pre-donation medical 
records are obtained from the transplant center. Post-donation medical records are obtained from the 
transplant center, as available, and from the participants’ medical providers over time. 
 
Aim 1: To assess emergency department utilization associated with caregiving among a cohort of 
living kidney donors who were obese at the time of donation. We will leverage an existing multi-center 
R01 study of a national cohort of obese living kidney donors, to quantify the association between a donor 
reporting that they served as the primary caregiver for the transplant recipient and ED utilization using 
generalized estimating equations. We will adjust for baseline characteristics and will explore the presence of 
effect modification and interaction between caregiving status and donor age, race/ethnicity, and rurality. 
 
Study population. The study population will consist of living donors with obesity identified by the parent R01, 
categorized by whether or not they served as the primary caregiver for their transplant recipient. Donors will be 
stratified by relationship to the recipient (parent, child, spouse/life partner, other caregiver) and sex to allow us 
to explore sex as a biological variable. We estimate that approximately 20% (n=5,070) were the caregiver for 
their recipient, of whom 40% were ≥ 50 years old (3% > 65 years), and 17% were minorities. 
 
Definition of caregiver. Donors are asked whether they served as the primary caregiver (i.e., the main 
individual who provided unpaid caregiving activities pre and post-donation) for their transplant recipient. 
 
Definition of outcome of interest. As part of the parent R01, healthcare utilization data are obtained from the 
questionnaire and include whether donors have utilized the ED since donation. Donors are asked to report not 
only whether they used the ED as well as the frequency of use.  
 
Aim 2: To assess hospitalization associated with caregiving among a cohort of living kidney donors 
who were obese at the time of donation. We will use the same cohort from Aim 1 to quantify the association 
between a donor reporting that they served as the primary caregiver for their transplant recipient and 
hospitalization using generalized estimating equations. 
 
Study population. The same study population identified in Aim 1 will be used. 
 
Definition of outcome of interest. The parent R01 also captures data on whether the donor has been 
hospitalized since donation and the number of times the donor has been hospitalized. 
 

STATISTICAL DESIGN AND POWER 
 
Aim 1. Power calculation. Goren et al. demonstrated a significant difference in ED utilization by caregiver 
status (7.2% for caregivers vs. 4.0% for non-caregivers).39 Assuming a two-tailed test and a proportion of 4% 
experiencing ED use in the non-caregiver group, we will have 99% power to detect a relative risk of 1.8 for ED 
utilization among caregivers vs. non-caregivers. This is likely an underestimate, given that individuals with 
obesity have a greater use of hospital services,33,34 and incidence is likely to be higher in our cohort. 
 
Aim 1. Statistical analyses. We will explore post-donation ED use by caregiver status, using generalized 
estimating equations (GEE) accounting for repeated measurements, to estimate whether odds of ED use differ 
by caregiver status. We will use Poisson regression to explore count of ED visits among those who report 
having used these services by caregiver status, adjusting for baseline characteristics, including demographic, 
socioeconomic, and health status at donation. We will explore the presence of effect modification and 
interaction between caregiving status and donor age, race/ethnicity, and rurality. As a sub-aim, we will explore 
whether utilization differs by self-reported physical, mental, and financial burden among caregiver donors. 
 
 
Aim 2. Power calculation. Goren et al. demonstrated a significant difference in the proportion of Alzheimer’s 
caregivers experiencing hospitalization (8.1% for caregivers vs. 5.1% for non-caregivers).39 Assuming a two-
tailed test and a proportion of 5% experiencing hospitalization in the non-caregiver group, we will have 99% 
power to detect a relative risk of 1.6 for hospitalization among caregivers vs. non-caregivers. This is likely an 
underestimate, given that this study was performed in Japan, and hospital admissions for many preventable 
diseases are higher in the United States than in other countries.40 
 
Aim 2. Statistical analyses. We will explore odds of post-donation hospitalization by caregiver status, first 
using generalized estimating equations to account for repeated measurements, then using Poisson regression 
to explore the counts of hospitalization among those who report having used these services. As in Aim 1, we 
will explore the presence of effect modification and interaction by stratification and interaction terms between 
caregiving status and donor age, ethnicity, and rurality, in addition to exploring the role of self-reported burden 
in hospitalization among the subset of caregiver donors. 
 
RESULTS 
Among 784 donors (median 10.4yrs post-donation), 148 (18.9%) identified as caregivers. Caregiver donors 
were older (62.6 vs. 57.9yrs, p< 0.001), more often female (69.6% vs. 58.3%, p=0.01), the recipient’s spouse 
(50.0% vs. 7.9%) or parent (16.2% vs. 4.6%, p< 0.001), and retired (38.4% vs. 24.9%, p=0.004), with no racial 
differences. Among those identifying as the caregiver and responding to the question about hospitalization 
(n=138), 71 (51.5%) reported having been admitted to the hospital since donation, compared to 237 (40.3%) 
among non-caregivers. Among those identifying as the caregiver and responding to the question about 
emergency room utilization since donation (n=144), 77 (53.5%) reported having been admitted to the hospital 
since donation, compared to 305 (49.4%) among non-caregivers.