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A Clinically Relevant Frailty Index for Aging Rats

Frailty is a clinical syndrome that is increasingly prevalent during aging. Frailty involves the confluence of reduced strength, speed, physical activity, and endurance and is associated with adverse health outcomes. The present study adapts existing clinical and preclinical indices of frailty to the Fischer (F344) rat. Male F344 rats (n = 133; 17 mo) completed a battery of behavioral tasks, including forelimb wire suspension (strength), rotarod (speed), open field (physical activity), and inclined screen (endurance). Rats that performed poorly (lowest quintile) on two tasks were considered mildly frail (17.29%, n = 23), and rats that performed poorly on 3-4 tasks were considered frail (2.26%, n = 3). Logistic regression of 100-day survival revealed that mildly frail rats were 3.8 times and frail rats were 27.5 times more likely to die during that period than nonfrail rats (p = .038; 95% confidence interval: 2.030, 372.564). The selected criterion tests, cutoff points, and index provide a potential tool for identifying frailty in aged F344 rats, which is consistent with existing frailty indices for humans and mice.