Skin-color-independent robust assessment of capillary refill time

Capillary Refill Time (CRT) is a visual method used to evaluate peripheral perfusion, particularly in low-resource environments. However, CRT’s repeatability and reproducibility are limited, particularly for dark-skinned individuals. This paper presents quantitative CRT measurements with good performance and repeatability for all Fitzpatrick skin phototypes. Tests were conducted on the forearm of 22 volunteers, using 7 kPa controlled compression, an RGB video camera, and white LED cross-polarized light. The CRT was determined by the time constant of an exponential regression to the green channel mean pixel intensity. An adaptive algorithm was developed to determine the best regression region to reduce noise, and incorrect and outlier CRT readings were flagged from the regression uncertainties. Results showed 80% of measurements were within 20% of the expected CRT value of a given volunteer, suggesting repeatable and reproducible quantitative CRT methods could be developed for robust measurements in patient triage, monitoring, and telehealth.