Racial and Sex Disparities in Catheter Use and Dialysis Access in the United States Medicare Population

Discussion

In this study, we evaluated the time spent on CVC as well as factors associated with transitioning to a permanent access in patients on incident dialysis starting on a CVC. We found that the average patient in the United States waited 220 days (approximately 7 months) on dialysis with a CVC before transitioning to a permanent access, despite the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative (KDOQI) and FFCL defining prolonged catheter use at ≥90 days.² Minorities and women spent longer time on CVC than whites and men, respectively. A common pattern seen across all races, ethnicities, and sexes was that those who had a maturing access site in place consistently spent less time on CVC. However, only 24.7% of patients had a maturing access in place at the time of HD initiation. In multivariate regression analysis, accounting for the competing risk of death, minorities were more likely to transition to a permanent access. However, blacks were the least likely to transition to an AVF as compared with whites, whereas Hispanics and other races were more likely to transition to AVF as compared with whites. Women were less likely to transition to an AVF and a permanent access in general compared with men. The disparities persisted in competing risk analysis of the subcohort with no maturing access in place. Women continued to have less likelihood of transition to AVF or a permanent access in general regardless of a maturing access in place at HD initiation, despite a survival advantage.

Although the FFCL initiative was mostly successful at increasing AVF prevalence, we have demonstrated that it has done so differentially across races, ethnicities, and sexes, with white and male patients being the most common recipient of this type of access creation. Our results also show that we continue to fall significantly short of one of its other main goals: decreased CVC use. More than 70% of the patients included in our analysis failed to transition off CVC during the 90-day window. The prolonged use of CVC has been controversial because of conflicting evidence from observational studies using various methodological techniques and the inability to conduct a randomized, controlled trial to answer these questions. CVC use has been shown to be associated with high infection rates,^5–7 rehospitalization,^8,9 and increased venous stenosis thereby affecting future dialysis access.^3,4 CVC use has also been shown to be more costly.^5,10–12 However, the relationship of CVC use to mortality is more complicated. In some publications, CVC has been shown to be associated with increased mortality.^5,9–11 For instance, Malas et al.¹⁴ showed dialysis initiation with an AVF was associated with a 37% reduction in 5-year mortality compared with CVC. In other studies, CVC use per se is not associated with increased mortality compared with AVF.²⁷ This complexity in CVC’s association with morbidity and mortality has been acknowledged by the 2019 KDOQI guidelines, which note that there is low to moderate evidence that most patients on incident HD starting dialysis through a CVC should be transitioned to permanent access to reduce the risk of bacteremia and other related infections, but there is insufficient evidence to make recommendations for transition to permanent access to reduce the risk of mortality, or that choice of incident vascular access type is associated with all-cause hospitalizations or mortality.²

In the 2017 USRDS Annual Data Report, 80% of the United States population used a CVC at hemodialysis initiation, and among all patients on incident dialysis, regardless of initial access, 68.4% were using a CVC at 90 days.¹ Our study sheds further light on the patients who initiate dialysis on CVC: only 28.3% transitioned to AVF/AVG at 90 days, 43.5% transitioned at 1 year, and 24.5% were deceased by 1 year. With such prolonged use of CVC and poor transition rates to AVF/AVG, we have shown that national efforts/policy should expand and better highlight the need for faster transitions off of CVCs. Compared with the mean 224 days spent on CVC for patients without a maturing access site, those with a maturing AVF spent 15 days less on CVC and those with a maturing AVG spent 28 days less on CVC. Our results are consistent with that of Leake et al.,²⁸ who found that AVGs were associated with fewer catheter days than AVFs. Having a maturing access in place did lead to shorter transition times in all race/ethnicity groups and in women, suggesting the role of pre-emptive dialysis access to reduce CVC time. However, a maturing access in place did not increase the likelihood of transition to an AVF for blacks or women, suggesting further research is needed in these subgroups.

Previous studies report more difficulty establishing successful access in blacks and women,^29,30 which suggests biologic reasons for these differences such as poor AVF maturation. However, the longer CVC time may also reflect system-related factors such as poor access to care as shown by other studies, as well as the lower rates of pre-ESKD nephrology care in blacks and Hispanics versus whites in our analysis.^31–33 Despite the higher likelihood of conversions to permanent access in general as shown in our study, black, Hispanic, and other racial groups still spent a longer time on CVC. This effect appears to be largely driven by a higher mortality in the white patient population and a greater likelihood to transition to AVG than whites. Similar to what was observed in Trivedi et al.,³⁴ in our study minorities are more often having AVGs as their first access created, as AVGs were the first access surgery in 27.2% of black patients, 19.9% of Hispanic patients, and 21.1% of other race patients compared with 16.5% of white patients. To address the possible biologic mediators of poor AVF maturation, we included advancing age in the model, which was associated with fewer AVF transitions and higher AVG use. We also used surrogate markers for frailty, such as underweight body mass index, poor activities of daily living, and institutionalization. All of these factors were associated with fewer transitions to AVF/AVG. Despite adjustment for these factors as well as other comorbidities that have been shown to affect fistula maturation,^35–37 the racial and sex differences persisted in our analysis, suggesting the possibility of a role for access to care in these disparities.

To analyze this aspect, we adjusted for annual household income, USRDS network, and rurality/geography in our competing risks model and, not unexpectedly, those in the lowest quartile income bracket had lower likelihood of transition to a permanent access, but there were no significant differences in transitions on the basis of increasingly rural location or USRDS network. Pre-ESKD nephrology care, in our analysis, increased the likelihood for transition to permanent access. Prior research shows that residential neighborhoods with higher black populations are associated with lower access to pre-ESKD nephrology care but not with quality of the nephrology care received.³¹ However, in our competing risk models, we adjusted for pre-ESKD nephrology care and found there to be decreased racial/ethnic disparities in transition to a permanent access likely because care had already been established and a plan for access creation in motion. When we stratified the regression analysis by sex, the effect of pre-ESKD care on likelihood to transition to AVF and AVG is similar between men and women (sHR, 1.33; 95% CI, 1.29 to 1.38 versus sHR, 1.34; 95% CI, 1.30 to 1.39) despite women spending a longer time on CVC. This is particularly interesting given that women had a higher prevalence of maturing access in place at the time of dialysis start compared with men.

In our subgroup analysis, women spent on average more days on CVC (230 days) compared with men (212 days) with a lower prevalence of maturing access in place at the time of starting hemodialysis. Women have been shown to be more likely to initiate dialysis on a CVC than men,³⁸ have greater use of AVG as first access,³⁴ and experience lower rates of fistula maturation.³⁶ Pre-ESKD care for women is poorly studied. In general, before the Affordable Care Act 2010, women were charged higher premiums by multiple insurance plans, but our analysis focuses on Medicare eligible population and that may be why there is more parity in pre-HD access creation in our analysis. There is data showing provider bias in later referral for RRT among women^20,39 and persistence of sex differences in incident AVF use after accounting for clustering within dialysis facilities.⁴⁰ Others have postulated perceived bias among providers that women’s vessels will be smaller despite objective data suggesting no difference in vein diameters.^19,41 The Dialysis Outcomes and Practice Patterns Study showed significant variability in sex-specific catheter use by country, suggesting opportunity for improvement in hemodialysis practices for women.²¹ Although women had a decreased likelihood of transitioning to permanent access, this effect is not uniform across races/ethnicities as white women were less likely to transition to permanent access compared with other races/ethnicities in the competing risks model. Interestingly, the increased likelihood of successful transition off CVC seen in black women may be secondary to transitioning to an AVG (sHR, 1.69; 95% CI, 1.58 to 1.82), whereas Hispanic women and women of other races have equally high likelihoods of transitioning off CVC to AVF or AVG. These patterns in transition are consistent across sex as both black men and women are more likely to transition to AVG and Hispanic men and women and men and women of other races are equally likely to transition to either AVF or AVG (Table 3). A recent review of the ideal arteriovenous access highlighted the inadequacy of existing data on the association of race/ethnicity with arteriovenous access outcomes, and studies that have been published demonstrate conflicting results, the combination of which making it difficult for providers to discriminate the optimal access strategy.⁴²

Despite the slower rate of transition off CVC, patients of black race, Hispanic ethnicity, and other racial groups had a survival advantage over whites in our study of the USRDS. This echoes the findings of Quinn et al.,⁴³ who suggest that staying on CVC may not be as deleterious as previously believed as the excess mortality observed in patients receiving therapy via a CVC was not deemed to be directly related to access complications, and this uncertainty is reflected in the 2019 KDOQI guidelines.² For instance, patients aged ≥65 years old have a 1.7 greater risk of AVF failure compared with younger patients,⁴⁴ and in elderly patients AVFs confer only modest risk reduction in AVG-related bacteremia, suggesting that perhaps in older patients AVG may be equivalent to AVF, when considering the competing risks of life expectancy, comorbidities, and personal goals of care.⁴⁵ Given the survival advantage seen, although we did not look at causes of mortality or infection rates in this study, our findings regarding AVG utilization begs the question of whether AVG is just as good or better than AVF in black and female patients, especially those with an unsuitable vein for AVF.

Our study has several limitations. Our analysis is restricted to the Medicare population to capture the longitudinal transitions of AV access in the first 3 months of dialysis for patients with incident CVC. We therefore cannot generalize our findings to a younger dialysis patient population. Also, the data for access use is derived from billing data and new modifiers were added in the 2010 Medicare billing change. However, this has been found to be concordant with the CMS 2728 form at start of dialysis, yet it may be prone to billing/coding errors.⁴⁶ We could not find permanent access creation Current Procedural Terminology codes for approximately 40% of the cohort, but they all did have data on transition to AVF/AVF in Medicare hemodialysis billing claims, suggesting either a different payer such as Medicare advantage or private payers or possible coding errors. Our model adjusted for comorbidity data derived from CMS Form 2728, but there is a potential misreporting or underreporting of comorbidities. A limitation of the USRDS data set is the lack of anatomic data and as such we must assume that the location and type of vascular access created (or not created) was on the basis of surgeons’ best clinical judgment as we do not have vessel characteristics. Additionally, although we used surrogates, such as age, comorbidities, activities of daily living, and institutionalization, to adjust for biologic and anatomic factors that may influence access maturation, there is a possibility for residual confounding, and we cannot completely account for provider bias.

In conclusion, contemporary United States Medicare patients starting dialysis on a CVC on average spent more than 7 months on dialysis through a CVC before transitioning to mature AVF/AVG, despite national efforts to limit prolonged catheter use. White patients spend less time on CVC compared with other racial and ethnic groups despite all other studied groups demonstrating a transition advantage to permanent access, but this seems to be largely driven by transitioning to AVG. However, men spend less time on CVC and have a greater likelihood of transitioning off CVC than women, although women have a higher likelihood to transition to AVG for permanent access. Future work should focus on understanding the system level and process mechanisms behind the prolonged CVC use in the United States and re-evaluating strategies to decrease time on CVC. Because prolonged catheter use is associated with decreased survival and failure of future access modalities, there is an urgent need for clinicians and policymakers to shift focus to minimizing catheter use for patients starting hemodialysis through CVC.