Evaluation of a Wearable Device for Continuous, Non-Invasive Monitoring of Hematocrit Levels in Hemodialysis Patients
Forrest Miller, David Kuraguntla
Alio, San Francisco, CA
INTRODUCTION: Maintenance of euvolemia is a major challenge for hemodialysis patients, who account for a combined 6.5M annual hospital days. Clinical outcomes could be improved, and healthcare costs lowered, by enabling better management of fluid status and anemia, which is common among ESRD patients. This study presents a novel wearable device, SmartPatch, that uses multi-wavelength photoplethysmography (PPG) and other sensors to measure blood hematocrit (Hct), a key metric for monitoring fluid status and anemia. The SmartPatch is a component of a novel Remote Monitoring System (RMS) that facilitates secure data transmission and analysis and generates actionable alerts. Data demonstrating the feasibility of the RMS were previously accepted for presentation at the cancelled 2020 SAVS Annual Meeting. The aim of this study was to evaluate the system’s ability to accurately and precisely measure Hct in a real-world dialysis setting.
METHODS: 14 ESRD patients with arteriovenous fistulae currently undergoing dialysis were recruited to participate in this study. Each of these patients had a SmartPatch device placed on the skin over their fistula at each of three dialysis sessions two weeks apart. Reference Hct measurements were taken immediately before and after the session, timed to coincide with SmartPatch data recordings. A total of 83 sets of multi-channel PPG data were recorded and analyzed to determine the accuracy and precision of Hct measurement.
RESULTS: The RMS measured Hct with root-mean-square error (RMSE) of 2.13 Hct compared to reference values obtained from a Sysmex XN-1000 blood analyzer. These results are shown in Figure 1. The standard deviations for each read on the same patient-with the same device-were computed and averaged, weighted by group size, as a measure of precision. The RMS measured Hct with a mean standard deviation of 1.15 Hct. These error and standard deviation values compare favorably to available point-of-care devices like the HemoCue Hb 201+, which has been reported to measure Hct with a mean of 4.32-4.81 Hct and standard deviation of 1.56-3.88 Hct.
CONCLUSIONS: The results of this study illustrate the ability of the wearable SmartPatch to non-invasively measure blood Hct in ESRD patients with AV fistulae, to a degree of accuracy and precision that may outperform available point-of-care methods. This study also demonstrated the efficacy of the end-to-end Remote Monitoring System. 
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