Large discordance between creatinine-based and cystatin C-based estimated glomerular filtration rates is associated with falls, hospitalizations, and death in older adults.

Background: Estimated glomerular filtration rate (eGFR) calculated using creatinine and cystatin C often differ in older adults. We hypothesized that older adults with cystatin-based eGFR (eGFRcys) values significantly lower than creatinine-based eGFR (eGFRcr) values may have higher risk for aging-related adverse outcomes, independent of kidney function.

Methods: We conducted a longitudinal cohort study of adults ≥65 years old from the Health and Retirement Study, a cohort of older American adults, to determine the relationship between eGFR discordance and aging-related adverse outcomes. We calculated eGFRcr and eGFRcys using baseline creatinine and cystatin C measurements. A large eGFR discordance was defined as eGFRcys >30% lower than eGFRcr. We assessed four aging-related adverse outcomes over a two-year follow-up: falls, hip fractures, hospitalizations, and death. We fit separate multivariable regression models to determine the association between having a large eGFR discordance and each outcome adjusting for confounders including kidney function.

Results: Of 5574 older adults, 1683 (30%) had a large eGFR discordance. Those with a large eGFR discordance were more likely to be older, female, and White. The prevalence of a large eGFR discordance increased with age, from 20% among those 65-69 years to 44% among those 80 years and older. Over a two-year follow-up, there were 305 deaths (5.5%), 2013 falls (39.2%), 69 hip fractures (1.3%), and 1649 hospitalizations (32.2%). In adjusted analyses, large eGFR discordance was associated with a higher hazard ratio for death (HR 1.43, 95% CI 1.12-1.82) and significantly higher odds of falls (odds ratio [OR] 1.32, 95% CI 1.16-1.51) and hospitalizations (OR 1.32, 95% CI 1.15-1.51). A large eGFR discordance was not associated with hip fractures.

Conclusion: In a large, nationally representative cohort of older adults, prevalence of eGFR discordance increased with age and was associated with higher risk of falls, hospitalization, and death, independent of kidney function.