Those patients with large varicose veins, symptomatic veins (achy legs, swelling, etc.), history of deep venous thrombosis or thrombophlebitis, and previous venous surgery should undergo vascular testing prior to sclerotherapy. The main reason is because those people with more severe venous disease do not respond well to sclerotherapy unless deeper venous disease is properly addressed. Also, there may be increased risk of adverse reactions to sclerotherapy.