If a person has had a blood clot already, should they receive blood thinners after upcoming surgery?

Variable: Blood clot where? Why- many causes from coagulopathies, to trauma to medications etc. What surgery? Ortho higher risk as an example. Full history and physical and risk benefit analysis with your PCP and the surgeon to get to an accurate recommendation.

Depends: Depends on where the clot was, how long ago, how many times you had clots. Also type of surgery will be important in deciding the need for prophylactic anti-coagulation.

Anticoagulation wise: Prophylactic anticoagulation would be helpful and probably indicated providing the type of surgery being performed would not be impacted negatively by the anticoagulation. Some individuals are prone to developing clots with the stress of surgery, so an ounce of prevention is wise.