The selection of candidates for ELA involves a directed history, physical examination, and duplex ultrasound (DUS) examination. 

The contraindications to endovenous treatment are listed below:

• Patients who are pregnant or breastfeeding (concerns related to anesthetic use and heated blood effluent that may pass through the placenta to the fetus)
• Obstructed deep venous system inadequate to support venous return after ELA
• Liver dysfunction or allergy making it impossible to use a local anesthetic (cold saline may be useful as an alternative)
• Allergy to both amide and ester local anesthetics (cold saline may be an alternative)
• Severe uncorrectable coagulopathy (ELA is safe with warfarin use if the international normalized ratio is between 2 and 3.) 
  
• Severe hypercoagulability syndromes (where risk of treatment outweighs potential benefits despite prophylactic anticoagulants)
• Inability to adequately ambulate after the procedure
• Sciatic vein reflux
• Thrombus or synechiae in the vein or tortuous vein making passage of an endovenous device impossible (unless multiple access points are chosen)

Treatment of incompetent superficial truncal veins in patients with previous deep vein thrombosis requires a careful assessment of the adequacy of the patent segments of the deep venous system. It also requires a risk stratification of postprocedural thrombosis. ELA is appropriate if the deep system is adequate enough to support venous drainage and the superficial venous incompetence is responsible for significant symptoms or skin changes. If the patient has an ongoing risk for thrombosis, ELA may still be appropriate if that risk can be sufficiently decreased with prophylactic anticoagulants. If saphenous reflux is seen with venous ulcers with an adequate deep venous system, ELA of the causative veins is necessary to minimize the risk of a recurrent ulceration.

Treatment of competent enlarged superficial venous segments has no proven medical benefit and should not be performed. In some cases, the enlarged vein may be functioning as a re-entry or collateral pathway for another source of reflux or deep vein obstruction. The use of ELA to close incompetent perforating veins has been described, and studies show a benefit in ulcer healing and recurrence.