PF4 and myalgic encephalomeyelitis/chronic fatigue syndrome: We identified three significant proteins related to the coagulation system that deserves discussion: thrombospondin-1; platelet factor 4; and vitamin K-dependent protein S. When interpreting these findings, there are a number of recently published articles implicating platelets and other components of and processes related to the coagulation system in ME/CFS cohorts [8, 22–24, 34, 35], as well as endothelial dysfunction [11–14, 16–18, 36].