Protein C or protein S deficiency is also sometimes suspected when a venous thromboembolism develops in an unusual site like the portal, mesenteric, or cerebral veins.
Protein C or S deficiency is suspected in people with a strong family history of coagulation disorders, especially those who suffer from recurrent venous thromboembolisms and experience their first thrombotic event before age fifty.
A more serious presentation is neonatal purpura fulminans, which is when a newborn with protein C or S deficiency suffers massive arterial and venous thromboembolisms with hemorrhagic skin necrosis.