Red Blood Cell Distribution Width Is Associated With Functional Outcomes Following Surgery for Hip Fracture

Elevated red blood cell distribution width (RDW) is increasingly found to be associated with adverse health outcomes in older adults. We leveraged a randomized clinical trial that was investigating responses to supervised exercise (EX) with or without a topical testosterone gel (T) following hip fracture surgery to evaluate the role of RDW as a biomarker predictive of musculoskeletal outcomes.

We conducted ancillary analyses of 105 women ( $\ge$  65 years) enrolled in the Starting a Testosterone and Exercise Program after Hip Injury (STEP-HI) clinical trial. Outcomes included muscle mass, strength measured by maximum hand grip strength and one-repetition maximum (1-RM) leg press, and physical performance assessed by six-minute walk distance, four-meter walk, and short physical performance battery (SPPB). Linear mixed-effects models were used to model each outcome at baseline, 3, and 6 months in each treatment group with baseline RDW.

In the EX+T treatment group only, we observed an inverse association between RDW and SPPB at baseline, 3, and 6 months (ß = -0.266 SD per 1% increase in RDW, 95% CI [-0.499, -0.033], p = 0.02) follow-up, as well as between RDW and 1-RM leg press at 3 and 6 months (ß = -0.437 SD per 1% increase in RDW, 95% CI [-0.737, -0.136], p = 0.002) follow-up.

Our findings suggest that lower RDW may be associated with greater functional benefit from a combination of supervised exercise and testosterone treatment after hip fracture surgery. These results support the concept of Precision Gerontology, which emphasizes the benefits of improving outcomes in older adults through improved targeting of inter-individual heterogeneity.