Cognitive function and the risk of death in chronic kidney disease

Abstract

Background and aims: Cognitive impairment is a risk factor for death in dialysis patients and the general population. We sought to determine if cognitive impairment is associated with death in people with non-dialysis-dependent chronic kidney disease (CKD), and if so, whether this relationship is greater in the CKD population compared to the general population.

Methods: National Health and Nutrition Examination Survey-III participants older than 60 years were asked to subtract 3 from 20 five times and to perform immediate and delayed recall of three items. A cognitive score of 0-11 was assigned based on the number of correct responses. Participants were categorized according to cognitive score (11, 9-10, 6-9, and 0-5) and CKD status. Survival analyses were conducted using Cox models.

Results: Within the CKD subpopulation, those in the lowest cognitive score group had a twofold increased hazard of death compared to those with maximum score. Within the non-CKD subpopulation, those in the lowest cognitive score group had a 46% increased hazard of death compared to those with maximum score. However, the difference in the hazards of death in the CKD and non-CKD subpopulations with the lowest cognitive score was not significant (p = 0.99).

Conclusions: Low cognitive score is associated with an increased risk of death in elderly individuals with and without CKD; however, there was no interaction of CKD and low cognitive score in this analysis.

Fig. 1

Stacked bar graph of the percentages of NHANES III participants older than 60 years of age in each cognitive score group in the non-CKD and CKD subpopulations. A lower percentage of those with CKD achieved the maximum cognitive score (11). Values for the non-CKD subpopulation do not add up to 100% due to rounding.

Fig. 2

Kaplan-Meier plots of the unadjusted probability of survival by cognitive score in the non-CKD subpopulation (a) and CKD subpopulation (b).

Fig. 3

Hazard of death according to cognitive score (CS) within the non-CKD and CKD subpopulations after adjusting for demographic factors, history of cardiovascular disease, hypertension, diabetes, physical inactivity, smoking, alcohol use, eGFR and albuminuria; stratified by gender and history of stroke. Separate Cox models were performed for each subpopulation. Those with the maximum cognitive score of 11 serve as the reference group within each subpopulation.