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

Key Points A large eGFR discordance ( i.e ., cystatin C–based eGFR >30% lower than creatinine-based eGFR) is common in older adults and increased with age. A large eGFR discordance was associated with increased risk of falls, hospitalization, and death, independent of kidney function. There are multiple ways to measure differences in creatinine and cystatin C; all produce similar associations with aging-related adverse outcomes. Background eGFR calculated using creatinine and cystatin C often differ in older adults. We hypothesized that older adults with cystatin C–based eGFR (eGFRcys) values significantly lower than creatinine-based eGFR (eGFRcr) values may have higher risk of aging-related adverse outcomes, independent of kidney function. Methods We conducted a longitudinal cohort study of adults 65 years and older 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 2-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 2-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 (hazard ratio, 1.43; 95% confidence interval [CI], 1.12 to 1.82) and significantly higher odds of falls (odds ratio, 1.32; 95% CI, 1.16 to 1.51) and hospitalizations (odds ratio, 1.32; 95% CI, 1.15 to 1.51). A large eGFR discordance was not associated with hip fractures. Conclusions 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.