Anna Agnes Lytzen

In understanding the pathophysiology of kidney disease, as well as the mechanisms and effects of novel treatments targeting the kidney, the assessment of glomerular filtration rate (GFR) has served as an invaluable index of kidney function for nearly a century. The indirect clinical evaluation of GFR through the measurement of serum creatinine remains one of the most frequently requested blood tests in hospitals worldwide to this day.

1 INTRODUCTION The post-acute sequelae of the SARS-CoV-2 infection presents a multifaceted challenge. More than 25% of individuals experience persistent exercise intolerance at 12-month follow-up with a concomitant reduction in peak oxygen uptake ( V ̇ O 2 peak ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{peak}}}}$ ) after the acute phase of the infection. Furthermore, 15% of individuals continue to have symptoms at 12 months (Foged et al., 2021; Gesser et al., 2023; Vos et al., 2022).

1 INTRODUCTION After the initial surge of the coronavirus disease 2019 (COVID-19) pandemic, it became evident that the pulmonary effects of the disease often lasted far beyond the immediate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (Crook et al., 2021).