OBJECTIVES: It is understood that microvascular dysfunction plays a key role in the pathogenesis of SARS-CoV-2 coronavirus disease (COVID-19). The aim of this study was to evaluate the usefulness of an automated, quantitative nailfold capillaroscopy system in identifying microvascular changes in those confirmed with or having had COVID-19. METHODS: Ninety-seven participants were enrolled into this study and grouped as follows: 52 participants with acute COVID-19 (further grouped by disease severity) and 45 participants with convalescent COVID-19 (further grouped into long COVID i.e. symptoms beyond 12 weeks, and fully recovered). Nailfold capillaroscopy images were obtained from the bilateral ring fingers using a Dino-Lite CapillaryScope 200 Pro, a small USB handheld microscope. Images were assessed quantitatively using bespoke automated measurement software and the number of haemorrhages noted for each participant. RESULTS: Capillaries were predominantly 'normal' in appearance with narrow capillary loops and evenly distributed, but with an increased number of haemorrhages (40 % in the convalescent group and 17 % in the acute group, p = 0.007). There was no statistically significant difference in the mean width of capillaries (20.9-21.8 μm) or vessel density (9.6-9.9 caps/mm
acute and convalescent group, respectively). CONCLUSIONS: This study has demonstrated the feasibility of nailfold capillaroscopy at the critical care bedside. Capillary structure appeared normal across all groups of individuals affected by COVID-19. Although the small differences in the microvasculature in recovered patients compared to in acutely unwell patients may suggest delayed structural change due to COVID-19, these differences are unlikely to be clinically relevant. Longitudinal studies would be required to explore this in more detail.