Disparities in Vascular Access: the role of social determinants
Written by: Katie Rizzolo, MD (@katierizzolo)
Racial and ethnic disparities in health outcomes and access to care exist at every level of kidney disease. In the United States, Black populations are 3.4 times more likely to develop end stage kidney disease compared with non-Hispanic White populations. Black populations have higher rates of chronic kidney disease (CKD) and have faster rates of progression to end stage kidney disease (ESKD). Black populations with kidney disease are less likely to have a timely pre-dialysis nephrology referral, are less likely to receive a kidney transplant or home dialysis therapies, and are less likely to dialyze with an arteriovenous fistula.
Amongst incident dialysis patients, 13.9% of Black patients initiate with a fistula compared with 16.6% of White patients. A greater number of Black patients initiate with AVG versus White patients: 4.5% compared with 2.5%. Amongst prevalent patients, 59.9% of Black patients dialyze with a fistula, compared with 68.8% of White patients (USRDS data). In a 2020 study looking at USRDS data from 2007-2014, Black and Hispanic patients were more likely to use a catheter as a bridge to AVF: 11% increased odds in Blacks and 9% increased odds in Hispanic/Latinx after adjusting for insurance status. Another study showed catheter use was similar between races in those who were not planning on a fistula or graft, indicating that the discrepancy in AVF/AVG use is mostly in those who, ideally, would receive an AVF/AVG.
Figure from USRDS data
Factors contributing to racial disparities in vascular access
The mechanisms contributing to racial differences in dialysis vascular access are multifactorial and exist in differences at the patient, provider, and healthcare system level.
At the patient level, gender, number of comorbidities, AVF characteristics are all associated with differences in use. Many studies have shown men are more likely to have an AVF compared with women. Hopson et al showed that in a short-term catheter use group, men were more likely to be waiting for AVF maturation, and less likely to be using a short-term catheter due to issues with AVG access. Comorbidities, such as heart failure, coronary artery disease, and peripheral arterial disease are well known operative risks and may interfere with fistula maturation. Diabetes is associated with primary fistula patency loss as well. However one study showed that at the dialysis system level, dialysis units with higher levels of comorbidities have similar numbers of AVFs and AVGs compared to those with fewer comorbidities; indicating that comorbidities may contribute to individual – not facility-decisions regarding vascular access.
Fistula characteristics may play a role in vascular access decisions. Some studies have shown fistulas in Black patients have lower patency and higher number of interventions. This leads to a larger number of Black patients using a catheter for short-term use due to graft maturation, inability to cannulate, or need for revisions. Amongst long-term dialysis patients using catheters in that study, a larger number of Black patients were utilizing catheters because all vascular access sites were exhausted (as opposed to waiting for AVF/AVG maturation). The underlying mechanisms behind these differences in vascular characteristics have not been fully examined and should be interpreted with caution. It is highly likely that social factors (such as healthcare access, delayed presentation to care) affect vascular characteristics leading to these outcomes, though this specifically has not been studied.
There are multiple steps to achieving a successful AVF: pre-dialysis care, surgical placement, successful maturation, and maintenance of patency. Irrespective of geographic area, Black patients receive less predialysis care, which corresponds to lower likelihood of starting dialysis with an AVF. One study, looking at incident versus delayed AVF starts, showed older Black patients were less likely to complete each step required to achieve a successful AVF: placement, successful use after placement, and maintenance of patency after successful use. The individual surgeon also plays an important role in the success of an AVF making it all the way to successful primary patency for dialysis. Studies have shown more frequent provider interactions and use of a vascular access coordinator improve rates of AVF placement.
Healthcare system level
Socioeconomic status, including insurance, has been associated with AVF access. US patients become eligible for Medicare in their fourth month of dialysis; around 12-20% of patients are uninsured around the time of dialysis initiation. As such, uninsured patients initiating dialysis with a catheter are less likely to receive a AVF/AVG by their fourth dialysis month compared with those on Medicaid or Medicare. Medicare patients are more likely to already be on dialysis at the time of AVF surgery in comparison to those with private insurance. Relatedly, individual and area-level poverty rates are associated with lower AVF use, as assessed by dual-eligibility status.
ESRD networks are associated with varying catheter use even after adjusting for patient demographics, race, sex, age, BMI and comorbidities. One study examining Medicare claims for first access placement between 2003-2008 showed rates of catheters were highest in metropolitan areas and AVFs highest in rural areas after adjusting for age, sex, race, primary ESRD cause, employment status and comorbidities. This suggests geographic disparities likely play a role in racial disparities observed in AVF use.
Geography and vascular access disparities
Prior research suggests vascular surgeons may be less likely to practice in socioeconomically disadvantaged areas, leading to potential racial disparities in AVF creation. The article in KI Reports by Zhang et al examined the association between racial disparities in AVF use and geographic variability in vascular surgeons. The authors utilized 2016-2017 USRDS and CROWNWeb data to extract and track the type of vascular access in use and compare with surgeon data extracted from Medicare claims. The data was then adjusted for demographic factors, facility characteristics, and sociodemographic conditions. Notably, they evaluated AVF use one year after dialysis initiation- which served to eliminate early barriers to AVF use (such as predialysis care and insurance status as described above).
The highest quartile of vascular surgeon supply included a lower proportion of Black patients, lower proportion of patients with lower socioeconomic status, higher prevalence of comorbidities, and higher rates of predialysis care. Areas with higher supply of surgeons were associated with increased likelihood of AVF use.
Higher AVF use was associated with higher BMI, HTN, predialysis nephrology care, and dialysis treatment at a large chain dialysis facility. Lower AVF use was associated with Black race, older age, and female gender. Areas of lower surgeon supply had higher proportions of Black patients.
However, higher surgeon supply did not necessarily lower racial disparities in AVF use. Compared with White patients, Black patients were 10% less likely to have successful AVF in low surgeon supply areas, compared with 8% less likely in high surgeon supply areas. Notably, higher surgeon supply also did not translate to more expeditious AVF use. The likelihood of AVF use within 12 months of hemodialysis use in those patients initiating with a catheter was only 4% higher in areas of higher surgeon supply. Surgeons in these areas performed fewer AVF per surgeon- which may explain why surgeon supply alone cannot predict increased AVF use.
The authors note three main findings:
Patients living in areas with higher surgeon supply had slightly higher adjusted likelihood of AVF use.
Black patients were less likely to live in areas with higher surgeon supply.
Higher surgeon supply did not lower the racial disparity in AVF use.
Visual abstract by Eric Au MD (@ericau)
Overall, this study adds to the growing compendium of studies exploring factors contributing to racial disparities in vascular access. A major strength was assessing use of AVF at 12 months, which serves to limit the effects of pre-dialysis care and insurance use on access use on dialysis initiation. Further, they included all patients, including younger patients who were not Medicare eligible at the time of initiation.
The underlying factors affecting vascular access and racial disparities are likely multifactorial with issues on the patient, provider, and system level. As the authors note, these large data sets are unable to evaluate the disparities in the process of achieving a fistula, or understand individual clinical or patient decision making regarding vascular access. Further understanding the social factors - such as economic, environmental, and living conditions which affect these policies, health care decisions, and outcomes- is crucial to understanding the layers of complexity surrounding disparities in vascular access care.