Cognitive Function among Patients Evaluated for Kidney Transplantation

Patients with kidney failure undergoing dialysis may develop cognitive impairment; the prevalence of cognitive impairment in this patient population ranges from 10% to 80%, depending on the specific population being studied and the test used to define it. Patients with dementia are contraindicated for kidney transplantation; however, transplant candidates may have undiagnosed mild cognitive impairment. Because kidney transplantation candidates are rarely screened for cognitive functioning, the proportion of candidates with cognitive impairment at the time of transplant evaluation and the effect on functional dependence are unknown. Intact cognition is critical for patients undergoing evaluation for kidney transplantation; cognitive impairment may spur difficulties navigating the complex medical system associated with transplantation. Cognitive impairment also presents challenges to patients in managing chronic conditions and adherence to complex medication regimens and fluid and dietary restrictions. Nadia M. Chu, PhD, MPH, and colleagues conducted a two-center prospective cohort study among dialysis patients undergoing evaluation for transplantation to examine (1) the prevalence of cognitive impairment and level of functional impairment and functional dependence in those with cognitive impairment, (2) the chance of listing for kidney transplantation and the rate of kidney transplantation by cognitive impairment status at the time of evaluation, and (3) the risk for kidney transplantation waitlist mortality. The associations were also examined based on diabetes status. Cognitive impairment was measured using the Modified Mini-Mental State Examination (3MS) at the time of kidney transplantation at the two centers. Cognitive impairment was defined as a 3MS score <80. The outcomes of interest were listing, waitlist mortality, and kidney transplantation. Results of the study were reported in the American Journal of Kidney Diseases [2020;76(1):72-81]. The study cohort included 3630 dialysis patients who were undergoing evaluation for kidney transplantation. Median age was 56 years, 41.2% were women, and 45.5% were Black. At the time of transplant evaluation, 6.4% of the participants were identified as having cognitive impairment. Those with cognitive impairment were more likely to be older (median age 62 vs 56 years; P<.001), Black (69.1% vs 43.8%; P<.001), have diabetes (49.5% vs 41.7%; P=.04), and lower educational attainment (75.5% vs 42.3%; P<.001), and were less likely to be women (30.0% vs 41.9%; P<.001), compared with those without cognitive impairment. There was an association between cognitive impairment at the time of kidney transplantation evaluation and functional dependence for both activities of daily living (ADLs) and instrumental activities of daily living (IADLs) (15.4% vs 7.7% in those with vs without impairment; P<.001, and 36.2% vs 19.4%; P<.001, respectively). Of the six ADL components, four were associated with cognitive impairment: difficulty with physical ambulation (10.0% vs 5.2% in those with vs without cognitive impairment; P=.004), dressing (4.7% vs 1.4%; P<.001), bathing (6.7% vs 2.2%; P<.001), and toileting (1.9% vs 0.6%; P=.03). There was an association between cognitive impairment and all eight of the IADL components: difficulty shopping (24.3% vs 9.5%; P<.001), washing (19.5% vs 7.7%; P<.001), taking transportation (13.8% vs 5.9%; P<.001), managing medications (13.8% vs 3.3%; P<.001), managing money (13.4% vs 2.6%; P<.001), cooking (13.3% vs 5.3%; P<.001), house cleaning (11.0% vs 5.1%; P<.001), and using the telephone (1.0% vs 0.1%; P=.007). The prevalence of cognitive impairment was 7.3% among patients with diabetes compared with 5.4% of patients without diabetes (P=.04). There were differences in the median scores of the different 3MS components by diabetes status: psychomotor skills (20 vs 21 points in those with vs without diabetes; P=.001), memory (19 vs 20 points; P<.001), and identification/association (23 vs 24 points; P=.001), There were no statistical differences in scores for orientation and concentration/calculation by diabetes status. Following adjustment for age, sex, race, education, diabetes and Charlson Comorbidity Index score, cognitively impaired participants had a 25% (adjusted hazard ratio [aHR], 0.75; 95% confidence interval [CI], 0.61-0.91) lower chance of being listed for kidney transplantation, compared with participants who were not cognitively impaired. This association nominally differed by sex at a borderline level of statistical significant (Pinteraction=.05): among male and female participants, aHRs for listing in those with versus without cognitive impairment were 0.55 (95% CI, 0.38-0.80) and 0.86 (95% CI, 0.68-1.08), respectively. This association did not differ by age, race/ethnicity, diabetes status, or functional dependence. Following adjustment, there was no association between cognitive impairment and the risk for waitlist mortality (adjusted subdistribution HR, 1.53; 95% CI, 0.83-2.18). However, this association varied by diabetes status (Pinteraction=.02). Among participants without diabetes, there was an association between cognitive impairment and a 2.47 times greater risk for waitlist mortality compared with participants without cognitive impairment. Among those with diabetes, there was no association between cognitive impairment and waitlist mortality. Among the cohort of kidney transplantation candidates, median follow-up time following listing for transplantation was 1.6 years. There was no difference by cognitive impairment in the cumulative incidence of kidney transplantation. In both unadjusted and adjusted analyses, there was no association between the rate of kidney transplantation and cognitive impairment. However, at borderline statistical significance, there was nominal variation in the association by diabetes status: among participants with and without diabetes, adjusted incidence rate ratios for kidney transplantation in those with versus without cognitive impairment were 0.58 (95% CI, 0.36-0.93) and 1.12 (95% CI, 0.71-1.77), respectively. Limitations to the study findings cited by the authors included the use of a single instrument to define cognitive impairment and the number of centers included in the analysis. “Cognitive impairment is associated with a lower change of being placed in the waitlist, and among patients without diabetes, with increased mortality on the waitlist. Future studies should investigate whether implementation of screening for cognitive impairment improves these outcomes,” the researchers said. Takeaway Points
  1. Researchers conducted a study to estimate the burden of cognitive impairment in patients being evaluated for kidney transplantation and its association with access to transplantation and waitlist mortality.
  2. In a prospective cohort study of patients being evaluated for transplantation, both with and without cognitive impairment, those with cognitive impairment had a 25% lower change of being waitlisted for transplant.
  3. There was a nominal difference by diabetes status for the association between cognitive impairment rate and kidney transplantation rate; candidates with diabetes and cognitive impairment were at 2.47 times greater risk for waitlist mortality.