SDC1 and COVID-19: Eleven studies compared syndecan-1 levels between patients with COVID-19 and healthy control subjects [15–25], three studies compared syndecan-1 levels between COVID-19 convalescents and healthy control subjects [24, 26, 27], while eight studies evaluate the association between syndecan-1 levels and complications of COVID-19 [19, 22, 23, 25, 28–31].