Serum cystatin C level can be an early predictor in community-living people? A clinical question to the conclusion

Dear Editor I read the recent article ‘Serum cystatin C level is associated with locomotive syndrome risk and can be an early predictor in community-living people: The Yakumo study’ [1] with great interest. This study evaluated the relationship between the 25-question geriatric locomotive function score (Locomo25) [2] and serum cystatin C level and reported a significant correlation between the two in patients aged ≥60 years, concluding that cystatin C level is an early predictor of locomotive syndrome (LS). While this is timely and an innovative study, I am afraid that its conclusion got ahead of itself for the reason as follows. Cystatin C is a protein encoded by the CST3 gene [3] that is widely used as a biomarker of renal function. It is well known that cystatin C correlates with aging, gender, and weight as well as serum creatinine level, and it is more closely correlated with aging [4]. Moreover, even in elderly people aged 64–100, its level has been shown to increase with age [5].