Over one in four adults over the age of 65 may have chronic kidney disease (CKD) defined as a reduced kidney function. While serum creatinine remains the most practical biomarker for estimation of kidney function because it is part of metabolic panels, other biomarkers such as cystatin C may be more informative; unlike creatinine, cystatin C is not influenced by muscle mass or function. As people age, muscle mass declines and this may influence the estimation of kidney function based on serum creatinine and it may influence frailty and falls. Dr. Potok and colleagues examined the difference in estimated kidney function based on cystatin C and serum creatinine in 9,029 adults with a mean age of 68 +/- 9 years enrolled in the Systolic Blood Pressure Intervention trial. The difference between kidney function measured with these two markers (cystatin C-based kidney function - creatinine-based kidney function) was associated with lower odds of frailty, falls, and cardiovascular disease events. These findings emphasize the fact that muscle mass and function influence serum creatinine values but do not influence serum cystatin C values. The investigators state that the difference in cystatin C- and creatinine-based kidney function could be used to predict adverse outcomes in older adults.