Establishing a common metric for physical function: Linking SARC-F and PROMIS® physical function

Aligned with the increasing need for standardized assessment of physical function in older individuals with cancer and other conditions, several patient-reported outcome measures (PROMs) have been developed and published. The aim of this study is to link the Strength, Assistance with walking, Rising from a chair, Climbing stairs, and Falls questionnaire (SARC-F), and the Patient-Reported Outcomes Measurement Information System® (PROMIS®) Physical Function Short Form 8c (PROMIS PF 8c), and make their scores convertible, in order to expand the use of both instruments in research and inform clinicians and researchers about the interchangeability of critical cut-off scores.

The sample included 300 participants recruited from an online panel. Participants were included if they had received a cancer diagnosis from a clinician and reported receiving anti-cancer treatment. We conducted five linking procedures and selected an optimal one to generate the crosswalk table between the two measures.

The linked T scores of all five methods showed acceptably small mean differences from the observed T scores, and the standard deviation (SD), and root-mean-squared deviation (RMSD) of the differences were generally similar across all methods. After comparing across all statistics, the Stocking-Lord approach was considered as the optimal approach to compute the crosswalk table for converting SARC-F raw scores to PROMIS PF 8c scores. The crosswalk table shows that the SARC-F cut-off value of 4 between healthy versus symptomatic with a corresponding score of 37 fell in the range of moderate physical function limitation from 30 to 39 on the PROMI PF 8c T score metric.

The linkage in this study has potential for improving clinical and research activities for people with cancer and perhaps others with a similar range of physical function. It facilitates the interpretability in scores of both measures on a common metric anchored on general population for further group-level analysis. Researchers can use this crosswalk to harmonize data collected from either instrument without requiring all cohorts to administer the same instrument for a prospective data collection or retrospective data analysis purpose or for a cross-study effectiveness study.