Specifically, the analysis showed that clinical symptomatology and NOx levels are key to distinguishing between patients and matched sedentary healthy controls, whereas the variance between ME/CFS and long COVID is explained largely by the two pro-inflammatory molecules, IL-6 and IL-1β, along with serpin E1 (PAI-1), considered an endothelial biomarker associated with senescence. This evidence concerns the gene SERPINE1 and myalgic encephalomeyelitis/chronic fatigue syndrome.