BACKGROUND:We aimed to determine the utility of a patient-reported outcome (PRO) as it relates to patient performed testing (PPT) for measuring functional status in multiple myeloma patients after autologous hematopoietic stem cell transplantation (auto-HCT). METHODS:Symptom interference on walking (a PRO) was measured by the MD Anderson Symptom Inventory (MDASI). PPT was assessed via 6-min walk test (6MWT). Mixed effects modeling was used to examine (1) the longitudinal relationship between the MDASI score and 6MWT distance and (2) the MDASI scores between patients who did or did not complete the 6WMT. Receiver operating characteristic (ROC) curve analysis was performed to quantify the construct validity of the PRO by differentiating performance status. RESULTS:Seventy-nine patients were included. Mean 6MWT distance significantly correlated with MDASI-walking interference score (PRO) over the first month of auto-HCT (est = 6.09, p = 0.006). There was a significantly higher completion rate for MDASI versus 6MWT at each time point (p < 0.01). Patients who completed the 6MWT reported less interference on walking during the study period (est = 1.61, p < 0.0001). Finally, the PRO demonstrated significant construct validity for measuring functioning status with MDASI-walking against ECOG-PS as the anchor (AUC = 0.77, 95% CI 0.60-0.94, p = 0.003). CONCLUSION:The PRO of MDASI-walking interference is a valid physical functioning measure, correlating with an objective functional measure (6MWT) in MM patients undergoing auto-HCT. As patients with poorer functional status during therapy are less likely to complete PPT, this PRO may offer a more practical quantitative measure of functioning in patients.