If the blood clot is clearly provoked (i.e., surgery or oral contraceptives) such testing is not routinely done as it will not change management. If it was unprovoked, testing of the autoimmune condition termed Anti-Phospholipid Antibody Syndrome (APAS) is appropriate as the presence of APAS would require the use of Warfarin as opposed to a direct oral anticoagulant (DOAC). Also, if you become pregnant and have a family history of blood clots you might want to get tested to decide if you need prophylaxis during pregnancy.