CST3 and Cognitive impairment: The Aging Brain Cohort (ABC) study, another large racially diverse study conducted in the United States, found that individuals with cystatin C serum levels >1.25 mg/L had 1.92 times higher odds of 7-year incident cognitive impairment with respect to those with cystatin C levels <1.0 mg/L (Yaffe et al., 2008).