Background: Consumer-based wearables are becoming more popular and provide opportunities to track individual’s clinical parameters remotely. However, literature about their criterion and known groups validity is scarce. Objective: This study aimed to assess the validity of the Fitbit Charge 4, a wrist-worn consumer-based wearable, to measure clinical parameters (i.e., daily step count, resting heart rate, heart rate variability, respiratory rate and oxygen saturation) in patients with COPD and healthy controls in free-living conditions in Belgium by comparing it with medical grade devices. Methods: Participants wore the Fitbit Charge 4 along with three medical grade devices: (1) Dynaport MoveMonitor for 7 days retrieving daily step count; (2) Polar H10 for 5 days retrieving resting heart rate, heart rate variability and respiratory rate and (3) Nonin WristOX2 3150 for 4 nights retrieving oxygen saturation. Criterion validity was assessed by investigating the agreement between day-by-day measures of the Fitbit Charge 4 and the corresponding reference devices. Known groups validity was assessed by comparing patients with COPD with healthy controls. Results: Data of 30 patients with COPD and 25 age- and gender-matched healthy controls resulted in good agreement between the Fitbit Charge 4 and the corresponding reference device for measuring daily step count (intraclass correlation coefficients (ICC2,1)=0.79 and ICC2,1=0.85, respectively), resting heart rate (ICC2,1=0.80 and ICC2,1=0.79, respectively) and respiratory rate (ICC2,1=0.84 and ICC2,1=0.77, respectively). The agreement for heart rate variability was moderate (healthy controls, ICC2,1=0.69) to strong (COPD, ICC2,1=0.87). The agreement in measuring oxygen saturation in patients with COPD was poor (ICC2,1=0.32). The Fitbit device overestimated daily step count and underestimated heart rate variability in both groups. While resting heart rate and respiratory rate were overestimated in healthy controls, no difference was observed in patients with COPD. Oxygen saturation was overestimated in patients with COPD. The Fitbit Charge 4 detected significant differences in daily step count, resting heart rate and respiratory rate between patients with COPD and healthy controls, similar to those identified by the reference devices, supporting known groups validity. Conclusions: Although the Fitbit Charge 4 shows mainly moderate to good agreement, measures of clinical parameters deviated from the reference devices, indicating that monitoring patients remotely and interpreting parameters requires caution. Differences in clinical parameters between patients with COPD and healthy controls that were measured by the reference devices were all detected by the Fitbit Charge 4.
